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Model Screws," R. E. Froude, F.R.S., Proc. Naval December 24 1908) which will relieve the aëronaut Architects, 1908).

of responsibility in this respect. Ease in starting and Among birds, those which fly continuously seldom stopping implies the power of flying, (at any rate, for have the ratio of weight to wing area more than 1 lb. a short time) at low velocities; while manæuvring per square foot, and in many cases, such as hawks capacity demands ready control of the angles at which and swallows, the ratio is something like $ lb. per the various supporting surfaces are presented to the square foot; but whatever the ratio may be, so air.

A. MALLOCK. long as the animal can only give out a limited amount of power proportional to its weight, a definite limit can be assigned to the size and weight of the body THE BRITISH ASSOCIATION AT WINNIPEG. which can sustain itself in flight by muscular action. If the weight of the wing increased directly as its AS

S we go to press the seventy-ninth annual meeting area such a limit would not exist. The weight of a

of the British Association is being opened at flock of birds, for example, is limited simply by the Winnipeg, under the presidency of Sir J. J. Thomson, numbers in the flock, and we only have to suppose the F.R.S., whose inaugural address is reprinted below. individuals to be connected by a light framework to Following our usual custom, the addresses of presiconvert the flock into a flying machine the wing dents of most of the sections will be published in weight of which is proportional to the wing area. To

future issues of NATURE, and also accounts of the a certain extent, the biplane flying machine carries scientific proceedings of the sections. out the same idea, but in most of the existing types

This is the fourth time the association has met outthe weight of the connecting framework must to a

side the British Isles, the previous occasions being great extent neutralise the reduction of weight which

Montreal (1884), Toronto (1897), and South Africa should accompany the reduced linear dimensions.

From what has been said it will be seen that so was very successful, the number of members and assolong as no engine was available which, with all ciates present being 1362. During the twelve years adjuncts, such as fuel supply, framing, and wings, that have since elapsed, great progress has been made could raise the total weight much faster than could

in all branches of science, and, though the people of an animal of the weight of the engine only, there Western Canada do not expect to contribute a very was no chance for the addition of fight to human large part to the scientific proceedings of the sections, accomplishments, and it is due to the advent of the they anticipate interest in many of the subjects to be internal-combustion engine that it is now possible to

dealt with or discussed. Much interest in the meetcarry air-borne loads of more than 1000 lb. To carry ing has been manifested in Canada and the United heavy loads with a moderate wing area requires large States, as well as on this side of the Atlantic. It is horizontal velocities, and in such machines as have estimated that between 400 and 500 members have succeeded the load per square foot generally exceeds gone to Winnipeg from Europe, and it is hoped that

the total number of members and associates attending The high velocity requisite is advantageous when the meeting will be at least 1500. the machine is launched and is pursuing a straight

Generous financial support towards the expenses of course, but it adds to the difficulties of starting and the meeting has been given by the Dominion Governstopping, and is a restriction on manœuvring power :

ment, the Government of Manitoba, and the city of that is, it increases the radius of the circle in which Winnipeg, while the western provinces and cities have the machine can turn. When a flying machine of agreed to defray the expenses of an excursion to the weight w travels in a circle of radius ï with velocity Pacific Coast of a party of about two hundred officew the centrifugal force, F, is wv2/rg, and if the plane bearers and distinguished guests of the association. of the circle is horizontal the upward component of the

Excursions have been arranged for Saturday, normal force on the wings is w, and hence the normal August 28, to points of interest in the vicinity of force is (wo+F%)} (nearly), and the inclination (B) of Winnipeg, including Stony Mountain and the munithe wings to the horizontal in the direction of is cipal stone quarries; Lake Winnipeg, St. Andrew's F/w.

Rapids, and Selkirk; the wheat fields of Manitoba ; The normal force on a straight course differs little the hydro-electric plant on the Winnipeg River. from W.

In flying in a horizontal curve, therefore, Members have also the opportunity of visiting various the normal force must be increased in the ratio industrial works in the city of Winnipeg. (w2+F)!/w if the velocity is to remain constant. To Evening receptions will be held by the Lieutenanteffect this the engine revolutions must be quickened

Governor at Government House, and by the loca: and the fore and aft trim of the wings altered. In executive committee. Garden-parties have beer. other words, it requires more power to fly in a curve arranged for several afternoons during the meeting than in a straight course at the same speed, although

including those to be given at the historic Lower Fort the increase is not important so long as F/w is smali.

Garry by the Commissioner of the Hudson's Bay For example, if v= 50 f.s. and 1=200 feet, Company, at the Provincial Agricultural College, and F/W=0'256, the increase of_power required is about by the Hon. Chief Justice Howell. 3 per cent., and B= 14°. For the same radius if v=100 f.s., F/w=1'56. The power required is 1'86

INAUGURAL ADDRESS BY PROF. SIR J. J. THOMSON, M.A., times that for the straight course, and B=56° about.

LL.D., D.Sc., F.R.S., PRESIDENT OF THE Association. I am not aware that any exact experiments have TWENTY-FIVE years ago a great change was made in the yet been made on the manæuvring capacity of flying practice of the British Association. From the foundation machines, but the subject will have to be carefully

of our Society until 1884 its meetings had always been investigated.

held in the British Isles; in that year, however, the The three most important lines along which the

Association met in Montreal, and a step was taken which

changed us from an Insular into an Imperial Association. development of fiying machines should be pursued are those relating to intrinsic stability, ease of starting

For this change, which now I think meets with nothing

but approval, Canada is mainly responsible. Men of and stopping, and manœuvring capacity. It is im- science welcome it for the increased opportunities it gives probable that any form is intrinsically stable at all them of studying under the most pleasant and favourable speeds, but automatic devices may be introduced (as conditions different parts of our Empire, of making new mentioned in my letters to NATURE of January 30 and friends; such meetings as these not only promote the

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.progress of science, but also help to strengthen the bonds indeed in some quarters it seems to be held that the chief which bind together the different portions of the King's duty of a schoolmaster, and the best test of his efficiency, Dominions.

is to make his boys get scholarships. The preparation This year, for the third time in a quarter of a century, for the scholarship too often means that about two years we are meeting in Canada. As if to give us an object before the examination the boy begins to specialise, and lesson in the growth of Empire, you in Winnipeg took from the age of sixteen does little else than the subject, the opportunity at Jur first meeting in Canada in 1884 be it mathematics, classics, or natural science, for which to invite our members to visit Manitoba and see for them- he wishes to get a scholarship; then, on entering the selves the development of the Province at that time. university, he spends three or four years studying the Those who were fortunate enough to be your guests then same subject before he takes his degree, when his real as well as now are confronted with a change which must life-work ought to begin. How has this training fitted seem to them unexampled and almost incredible. Great him for this work? I will take the case in which the cities have sprung up, immense areas have been converted system might perhaps be expected to show to greatest from prairies to prosperous farms, flourishing industries advantage, when his work is to be original research in have been started, and the population has quadrupled. As the subject he has been studying. He has certainly the President of a scientific association I hope I may be acquired a very minute acquaintance with his subjectpardoned if I point out that even the enterprise and energy indeed, the knowledge possessed by some of the students of your people and the richness of your country would trained under this system is quite remarkable, much greater have been powerless to effect this change without the than that of any other students I have ever met. But resources placed at their disposal by the labours of men though he has acquired knowledge, the effect of studyof science.

ing one subject, and one subject only, for so long a time The eminence of my predecessors in the chair at the is too often to dull his enthusiasm for it, and he begins meetings of the British Association in Canada makes my research with much of his early interest and keenness task this evening a difficult one. The meeting at Montreal evaporated. Now there is hardly any quality was presided over by Lord Rayleigh, who, like Lord essential to success in research than enthusiasm. Research Kelvin, his colleague' in the chair of Section A at that is difficult, laborious, often disheartening. The carefully meeting, has left the lion's mark on every department designed apparatus refuses to work, it develops defects of physics, and has shown that, vast as is the empire which may take months of patient work to rectify, the of physics, there are still men who can extend its frontiers results obiained may appear inconsistent with each other in all of the many regions under its sway. It has been and with every known law of Nature, sleepless nights and my lot to succeed Lord Rayleigh in other offices as laborious days may seem only to make the confusion well as this, and I know how difficult a man he is to more confounded, and there is nothing for the student to follow.

do but to take for his motto “ It's dogged as does it,” The President of the second meeting in Canada-that and plod on, comforting himself with the assurance that held in 1897 at Toronto—was Sir John Evans, one of when success does come, the difficulties he has overcome those men who, like Boyle, Cavendish, Darwin, Joule, and will increase the pleasure--one of the most exquisite men Huggins, have, from their own resources and without the can enjoy—of getting some conception which will make aid derived from official positions or from the universities, all that was tangled, confused, and contradictory clear and made memorable contributions to science : such men form consistent. Unless he has enthusiasm to carry him on one of the characteristic features of British science. May when the prospect seems almost hopeless and the labour we not hope that, as the knowledge of science and the and strain incessant, the student may give up his task interest taken in it increase, more of the large number and take to easier, though less important, pursuits. of men of independent means in our country may be found I am convinced that no greater evil can be done to a working for the advancement of science, and thereby young man than to dull his enthusiasm. In a very conrendering services to the community no less valuable than siderable experience of students of physics beginning, rethe political, philanthropic, and social work at which many search, I have met with more-many more-failures from of them labour with so much zeal and success?

lack of enthusiasm and determination than from any lack I can, however, claim to have some experience of, at of knowledge or of what is usually known as cleverness. any rate, one branch of Canadian science, for it has been This continual harping from an early age on one submy privilege to receive at the Cavendish Laboratory many ject, which is so efficient in quenching enthusiasm, is students from your universities. Some of these have been much encouraged by the practice of the colleges to give holders of what are known as the 1851 scholarships. scholarships for proficiency in one subject alone. I went These scholarships are provided from the surplus of the through a list of the scholarships awarded in the UniGreat Exhibition of 1851, and are placed at the disposal versity of Cambridge last winter, and, though there were of most of the younger universities in the British Empire, 202 of them, I could only find three cases in which it was to enable students to devote themselves for two or three specified that the award was made for proficiency in more years to original research in various branches of science. than one subject. i have had many opportunities of seeing the work of The premature specialisation fostered by the preparation these scholars, and I should like to put on record my for these scholarships injures the student by depriving opinion that there is no educational endowment in the him of adequate literary culture, while when it extends, country which has done or is doing better work.

as it often does, to specialisation in one or two branches I have had, as I said, the privilege of having as pupils of science, it retards the progress of science by tending students from your universities as well as from those of to isolate one science from another. The boundaries New Zealand, Australia, and the United States, and have between the sciences are arbitrary, and tend to disappear thus had opportunities of comparing the effect on the as science progresses. The principles of one science often best men of the educational system in force at your find most striking and suggestive illustrations in the universities with that which prevails in the older English phenomena of another. Thus, for example, the physicist universities. Well, as the result, I have come to the con- finds in astronomy that effects he has observed in the clusion that there is a good deal in the latter system laboratory are illustrated on the grand scale in the sun which you have been wise not to imitate. The chief evil and stars. No better illustration of this could be given from which we at Cambridge suffer and which you have than Prof. Hale's recent discovery of the Zeeman effect avoided is, I am convinced, the excessive competition for in the light from sun-spots ; in chemistry, too, the physicist scholarships which confronts our students at almost every finds in the behaviour of whole series of reactions illustrastage of their education. You may form some estimate tions of the great laws of thermodynamics, while if he of the prevalence of these scholarships if I tell you that turns to the biological sciences he is confronted by the colleges in the University of Cambridge alone give problems, mostly unsolved, of unsurpassed interest. Conmore than 35,000l. a year in scholarships to under- sider for a moment the problem presented by almost any graduates, and I suppose the case is much the same at plant-the characteristic and often exquisite detail of Oxford. The result of this is that preparation for these fower, leaf, and habit—and remember that the mechanism scholarships dominates the education of the great majority which controls this almost infinite complexity was once of the cleverer boys who come to these universities, and contained in a seed perhaps hardly large enough to be visible. We have here one of the most entrancing problems the two. In part, too, it may be due to the fact that in chemistry and physics it is possible to conceive.

the problems with which the applied mathematician has Again, the specialisation prevalent in schools often pre- to deal are exceedingly difficult, and many may have felt vents students of science from acquiring sufficient know- that the problems presented by the older physics have been ledge of mathematics; it is true that most of those who worked over so often by men of the highest genius that study physics do some mathematics, but I hold that, in there was but little chance of any problem which they general, they do not do enough, and that they are not could have any hope of solving being left. as efficient physicists as they would be if they had a But the newer developments of physics have opened wider knowledge of that subject. There seems at present virgin ground which has not yet been worked over, and a tendency in some quarters to discourage the use of which offers problems to the mathematician of great mathematics in physics; indeed, one might infer, from interest and novelty-problems which will suggest and the statements of some writers in quasi-scientific journals, require new methods of attack, the development of which that ignorance of mathematics is almost a virtue. If this will advance pure mathematics as well as physics. is so, then surely of all the virtues this is the easiest and I have alluded to the fact that pure mathematicians most prevalent.

have been indebted to the study of concrete problems for I do not for a moment urge that the physicist should the origination of some of their most valuable conceptions ; confine himself to looking at his problems from the mathe- but though no doubt pure mathematicians are in many matical point of view; on the contrary, I think a famous ways very exceptional folk, yet in this respect they are French mathematician and physicist was guilty of only very human, Most of us need to tackle some definite slight exaggeration when he said that no discovery was difficulty before our minds develop whatever powers they really important or properly understood by its author may possess. This is true for even the youngest of us, unless and until he could explain it to the first man he for our schoolboys and schoolgirls, and I think the met in the street.

moral to be drawn from it is that we should aim at But two points of view are better than one, and the making the education in our schools as little bookish an) physicist who is also a mathematician possesses a most as practical and concrete as possible. powerful instrument for scientific research with which I once had an illustration of the power of the concrete many of the greatest discoveries have been made ; for ex- in stimulating the mind which made a very lasting ample, electric waves were discovered by mathematics impression upon me. One of my first pupils came to me long before they were detected in the laboratory. He has with the assurance from his previous teacher that he also at his command a language clear, concise, and knew little and cared less about mathematics, and that universal, and there is no better way of detecting ambigui- he had no chance of obtaining a degree in that subject. ties and discrepancies in his ideas than by trying to express For some time I thought this estimate was correct, but them in this language. Again, it often happens that we he happened to be enthusiastic about billiards, and when are not able to appreciate the full significance of some we were reading that part of mechanics which deals with physical discovery until we have subjected it to mathe- the collision of elastic bodies I pointed out that many of matical treatment, when we find that the effect we have the effects he was constantly observing were illustrations discovered involves other effects which have not been of the subject we were studying. From that time he was detected, and we are able by this means to duplicate the a changed man. He had never before regarded mathediscovery. Thus James Thomson, starting from the fact matics as anything but a means of annoying innocent that ice floats on water, showed that it follows by mathe- undergraduates; now, when he saw what important results matics that ice can be melted and water prevented from it could obtain, he became enthusiastic about it, developed freezing by pressure. This effect, which was at that time very considerable mathematical ability, and, though he had unknown, was afterwards verified by his brother, Lord already wasted two out of his three years at college, took Kelvin. Multitudes of similar duplication of physical dis

a good place in the Mathematical Tripos. coveries by mathematics could be quoted.

It is possible to read books, to pass examinations withI have been pleading in the interests of physics for a out the higher qualities of the mind being called into play. greater study of mathematics by physicists. I would also Indeed, I doubt if there is any process in which the mind plead for a greater study of physics by mathematicians in is: more quiescent than in reading without interest. 1 the interest of pure mathematics.

mnight appeal to the widespread habit of reading in bed The history of pure mathematics shows that many of as a prevention of insomnia as a proof of this. But it is the most important branches of the subject have arisen not possible for a boy to make a boat or for a girl to from the attempts made to get a mathematical solution of cook’ a dinner without using their brains. With practical a problem suggested by physics. Thus the differential things the difficulties have to be surmounted, the boat calculus arose from attempts to deal with the problem of must be made watertight, the dinner must be cooked, moving bodies. Fourier's theorem resulted from attempts while in reading there is always the hope that the difficu!. to deal with the vibrations of strings and the conduction

ties which have been slurred over will not be set in the of heat : indeed, it would seem that the most fruitful examination. crop of scientific ideas is produced by cross-fertilisation

I think it was Helmholtz who said that often in the between the mind and some definite fact, and that the

course of a research more thought and energy were spent mind by itself is comparatively unproductive.

in reducing refractory piece of brass to order than in I think, if we could trace the origin of some of our devising the method or planning the scheme of campaign. most comprehensive and important scientific ideas, it This constant need for thought and action gives to would be found that they arose in the attempt to find an original research in any branch of experimental science explanation of some apparently trivial and very special

great educational value even for those who will not become phenomenon ; when once started the ideas grew to such professional men of science. I have had considerable exgenerality and importance that their modest origin could perience with students beginning research in experimental hardly be suspected. Water vapour we know will refuse physics, and I have always been struck by the quite reto condense into rain unless there are particles of dust to markable improvement in judgment, independence of form nuclei ; so an idea before taking shape seems to re

thought and maturity produced by a year's research. quirr a nucleus of solid fact round which it can condense.

Research develops qualities which are apt to atrophy when I have ventured to urge the closer union between mathe- the student is preparing for examinations, and, quite apart matics and physics, because I think of late vears there

from the addition of new knowledge to our store, is of has heen some tendency for these sciences to drift apart, the greatest importance as a means of education. and that the workers in applied mathematics are relatively It is the practice in many universities to make special frwer than they were some years ago.

This is no doubt provision for the reception of students from other universidur to some extent to the remarkable developments made ties who wish to do original research or to study the more in the last few years in experimental physics on the one advanced parts of their subject, and considerable numbers hand and in the most abstract and metaphysical parts

of such students migrate from one university to another. of pure mathematics on the other. The fascination of I think it would be a good thing if this practice were to these has drawn workers to the frontiers of these regions extend to students at an earlier stage in their career : who wnild o-herwise' have worked nearer the junction of especially should I like to see a considerable interchange

of students between the universities in the Mother Country they move under an electric force, the rate at which the and those in the Colonies.

oppositely charged ones recombine, and these investigaI am quite sure that many of our English students, tions have thrown a new light, not only on electricity, especially those destined for public life, could have no but also on the structure of matter. more valuable experience than to spend a year in one or We know from these investigations that electricity, like other of your universities, and I hope some of your students matter, is molecular in structure, that just as a quantity might profit by a visit to ours.

of hydrogen is a collection of an immense number of I can think of nothing more likely to lead to a better small particles called molecules, so a charge of electricity understanding of the feelings, the sympathies, and, what is made up of a great number of small charges, each of is not less important, the prejudices, of one country by a perfectly definite and known amount. another, than by the youths of those countries spending Helmholtz said in 1880 that in his opinion the evidence a part of their student life together. Undergraduates as in favour of the molecular constitution of electricity was a rule do not wear a mask either of politeness or any even stronger than that in favour of the molecular conother material, and have probably a better knowledge of stitution of matter. How much stronger is that evidence each other's opinions and points of view—in fact, know now, when we have measured the charge on the unit and each other better than do people of riper age. To bring found it to be the same from whatever source the electricity this communion of students about there must be coopera- is obtained. Nay, further, the molecular theory of matter, tion between the universities throughout the Empire; is indebted to the molecular theory of electricity for the there must be recognition of each other's examinations, most accurate determination of its fundamental quantity, residence, and degrees. Before_this can be accomplished the number of molecules in any given quantity of an there must, as my friend. Mr. E. B. Sargant pointed out elementary substance. in a lecture given at the McGill University, be coopera- The great advantage of the electrical methods for the tion and recognition between the universities in each part study of the properties of matter is due to the fact that of the Empire. I do not mean for a moment that all whenever a particle is electrified it is very easily identified, universities in a country should be under one government. whereas an uncharged molecule is most elusive; and it is I am a strong believer in the individuality of universities, only when these are present in immense numbers that we but I do not think this is in any way inconsistent with are able to detect them. A very simple calculation will the policy of an open door from one university to every illustrate the difference in our power of detecting electrified other in the Empire.

and unelectrified molecules. The smallest quantity of unIt has usually been the practice of the President of this electrified matter ever detected is probably that of neon, Association to give some account of the progress made in one of the inert gases of the atmosphere. Prof. Strutt the last few years in the branch of science which he has has shown that the amount of neon in 1/20th of a cubic the honour to represent.

centimetre of the air at ordinary pressures can be detected I propose this evening to follow that precedent and to by the spectroscope ; Sir William Ramsay estimates that attempt to give a very short account of some of the the neon in the air only amounts to one part of neon in more recent developments of physics, and the new concep- 100,000 parts of air, so that the neon in 1/20th of a cubic tions of physical processes to which they have led.

centimetre of air would only occupy at atmospheric pressure The period, which has elapsed since the Association last a volume of half a millionth of a cubic centimetrę. When met in Canada has been one of almost unparalleled activity stated in this form the quantity seems exceedingly small, in many branches of physics, and many new and un- but in this small volume there are about ten million million suspected properties of matter and electricity have been molecules. Now the population of the earth is estimated discovered. The history of this period affords a remark- at about fifteen hundred millions, so that the smallest able illustration of the effect which may be produced by a number of molecules of neon we can identify is about 7,000 single discovery; for it is, I think, to the discovery of times the population of the earth. In other words, if we the Röntgen rays that we owe the rapidity of the progress

had no better test for the existence of a man than we which has recently been made in physics. A striking have for that of an unelectrified molecule we should come discovery like that of the Röntgen rays acts much like to the conclusion that the earth is uninhabited. Contrast the discovery of gold in a sparsely populated country; it this with our power of detecting electrified molecules. We attracts workers who come in the first place for the gold, can by the electrical method, even better by the cloud but who may find that the country has other products,

method of C. T. R. Wilson, detect the presence of three other charms, perhaps even more valuable than the gold or four charged particles in a cubic centimetre. Rutheritself. The country in which the gold was discovered in ford has shown that we can detect the presence of a single the case of the Röntgen rays was the department of a particle. Now the a particle is a charged atom of physics dealing with the discharge of electricity through helium; if this atom had been uncharged we should have, gases, a subject which, almost from the beginning of required more than a million million of them, instead of electrical science, had attracted a few enthusiastic workers, one, before we should have been able to detect them. who felt convinced that the key to unlock the secret of We may, I think, conclude, since electrified particles electricity was to be found in a vacuum tube. Röntgen, can be studied with so much greater ease than unelectrified in 1895, showed that when electricity passed through such ones, that we shall obtain a knowledge of the ultimate a tube, the tube emitted rays which could pass through structure of electricity before we arrive at a corresponding bodies opaque to ordinary light; which could, for example, degree of certainty with regard to the structure of matter. pass through the flesh of the body and throw a shadow We have already made considerable progress in the task of the bones on a suitable screen. The fascination of of discovering what the structure of electricity is. We this discovery attracted many workers to the subject of have known for some time that of one kind of electricity the discharge of electricity through gases, and led to -the negative-and a very interesting one it is. We great improvements in the instruments used in this type know that negative electricity, is made up of units all of of research. It is not, however, to the power of probing which are of the same kind ; that these units are exceeddark places, important though this is, that the influence ingly small compared with even the smallest atom, for of Röntgen rays on the progress of science has mainly the mass of the unit is only 1/1700th part of the mass of been due ; . it is rather because these rays make gases, an atom of hydrogen ; that its radius is only 10-13 centiand, indeed, solids and liquids, through which they pass metre, and that these units, “corpuscles as they have conductors of electricity. It is true that before the dis- been called, can be obtained from all substances. The size covery of these rays other methods of making gases con- of these corpuscles is on an altogether different scale from ductors were known, but none of these was so convenient that of atoms; the volume of a corpuscle bears to that for the purposes of accurate measurement.

of the atom about the same relation as that of a speck The study of gases exposed to Röntgen rays has revealed of dust to the volume of this room. Under suitable conin such gases the presence of particles charged with elec- ditions they move at enormous speeds, which approach in tricity; some of these particles are charged with positive, some instances the velocity of light. others with negative electricity.

The discovery of these corpuscles is an interesting exThe properties of these particles have been investigated : ample of the way Nature responds to the demands made we know the charge they carry, the speed with which upon her by mathematicians. Some years before the disa

covery of corpuscles it had been shown by a mathematical to be certain that the unit of positive electricity has been investigation that the mass of a body must be increased isolated, for we have to be on our guard against its being by a charge of electricity. This increase, however, is a much smaller body attached to the hydrogen atoms greater for small bodies than for large ones, and even which happen to be present in the vessel. "If the positive bodies as small as atoms are hopelessly too large to show units have a much greater mass than the negative ones, any appreciable effect; thus the result seemed entirely they ought not to be so easily deflected by magnetic forces academic. After a time corpuscles were discovered, and when moving at equal speeds; and in general the insensithese are so much smaller than the atom that the increase bility of the positive particles to the influence of a magnet in mass due to the charge becomes not merely appreciable, is very marked, though there are cases when the positive but so great that, as the experiments of Kaufmann and particles are much more readily deflected, and these have Bucherer have shown, the whole of the mass of the cor- been interpreted as proving the existence of positive units puscle arises from its charge.

comparable in mass with the negative ones. I have found, We know a great deal about negative electricity; what however, that in these cases the positive particles are do we know about positive electricity? Is positive elec- moving very slowly, and that the ease with which they tricity molecular in structure? Is it made up into units, are deflected is due to the smallness of the velocity and each unit carrying a charge equal in magnitude though not to that of the mass. It should, however, be noted opposite in sign to that carried by a corpuscle? Does, that M. Jean Becquerel has observed in the absorption or does not, this unit differ, in size and physical proper- spectra of some minerals, and Prof. Wood in the rotation ties, very widely from the corpuscle? We know that by of the plane of polarisation by sodium vapour, effects suitable processes we can get corpuscles out of any kind which could be explained by the presence in the substances of matter, and that the corpuscles will be the same from of positive units comparable in mass with corpuscles. whatever source they may be derived. Is a similar thing This, however, is not the only explanation which can true for positive electricity? Can we get, for example, be given of these effects, and at present the smallest a positive unit from oxygen of the same kind as that we positive electrified particles of which we have direct exget from hydrogen?

perimental evidence have masses comparable with that of For my own part, I think the evidence is in favour of an atom of hydrogen. the view that we can, although the nature of the unit of A knowledge of the mass and size of the two units of positive electricity makes the proof much more difficult electricity, the positive and the negative, would give us than for the negative unit.

the material for constructing what may be called a moleIn the first place we find that the positive particles, cular theory of electricity, and would be a starting-point

canalstrahlen is their technical name—discovered by for a theory of the structure of matter; for the most our distinguished guest, Dr. Goldstein, which are found natural view to take, as a provisional hypothesis, is that when an electric discharge passes through a highly rarefied matter is just a collection of positive and negative units gas, are, when the pressure is very low, the same, what- of electricity, and that the forces which hold atoms and ever may have been the gas in the vessel to begin with. molecules together, the properties which differentiate one If we pump out the gas until the pressure is too low to kind of matter from another, all have their origin in the allow the discharge to pass, and then introduce a small electrical forces exerted by positive and negative units of quantity of gas and restart the discharge, the positive electricity, grouped together in different ways in the atoms particles are the same whatever kind of gas may have of the different elements. been introduced.

As it would seem that the units of positive and negative I have, for example, put into the exhausted vessel electricity are of very different sizes, we must regard oxygen, argon, helium, the vapour of carbon tetrachloride, matter as a mixture containing systems of very different none of which contain hydrogen, and found the positive types, one type corresponding to the small corpuscle, the particles to be the same as when hydrogen was introduced. other to the large positive unit.

Some experiments made lately. by Wellisch, in the Since the energy associated with a given charge is Cavendish Laboratory, strongly support the view that there greater the smaller the body on which the charge is conis a definite unit of positive electricity independent of the centrated, the energy stored up in the negative corpuscles gas from which it is derived; these experiments were on will be far greater than that stored up by the positive. the velocity with which positive particles move through The amount of energy which is stored up in ordinary mixed gases. If we have a mixture of methyl-iodide and matter in the form of the electrostatic potential energy hydrogen exposed to Röntgen rays, the effect of the rays of its corpuscles is, I think, not generally realised. All on the methyl-iodide is so much greater than on the substances give out corpuscles, so that we may assume hydrogen that, even when the mixture contains only a that each atom of a substance contains at least one cor. small percentage of methyl-iodide, practically all the elec- puscle. From the size and the charge on the corpuscle, tricity comes from this gas, and not from the hydrogen. both of which are known, we find that each corpuscle

Now if the positive particles were merely the residue has 8x10-? ergs of energy; this is on the supposition left when a corpuscle had been abstracted from the methyl- that the usual expressions for the energy of a charged iodide, these particles would have the dimensions of a body hold when, as in the case of a corpuscle, the charge molecule of methyl-iodide; this is very large and heavy,

is reduced to one unit. Now in one gram of hydrogen and would therefore

more slowly through the there are about 6x 1025 atoms, so if there is only one hydrogen molecules than the positive particles derived from corpuscle in each atom the energy due to the corpuscles hydrogen itself, which would, on this view, be of the size in a gram of hydrogen would be 48 x 1016 ergs, or in x 10° and weight of the light hydrogen molecules. Wellisch calories. This is more than seven times the heat defound that the velocities of both the positive and negative veloped by one gram of radium, or than that developed by particles through the mixture were the same as the veloci- the burning of five tons of coal. Thus we see that even ties through pure hydrogen, although in the one case ordinary matter contains enormous stores of energy; this the ions had originated from methyl-iodide and in the other energy is fortunately kept fast bound by the corpuscles; from hydrogen ; a similar result was obtained when carbon if at any time an appreciable fraction were to get free tetrachloride, or mercury methyl, was used instead of the earth would explode and become a gaseous nebula. methyl-iodide. These and similar results lead to the con- The matter of which I have been speaking so far is the clusion that the atom of the different chemical elements material which builds up the earth, the sun, and the stars, contains definite units of positive as well as of negative the matter studied by the chemist, and which he can reelectricity, and that the positive electricity, like the present by a formula; this matter occupies, however, but negative, is molecular in structure.

an insignificant fraction of the universe, it forms but The investigations made on the unit of positive electricity minute islands in the great ocean of the æther, the subshow that it is of quite a different kind from the unit of stance with which the whole universe is filled. negative, the mass of the negative unit is exceedingly The æther is not a fantastic creation of the speculative small compared with any atom, the only positive units philosopher; it is as essential to us as the air we breathe. that up to the present have been detected are quite com- For we must remember that we on this earth are not parable in mass with the mass of an atom of hydrogen ; living on our own resources; we are dependent from in fact they seem equal to it. This makes it more difficult minute to minute upon what we are getting from the

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