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only different developments of the same fundamental clear sketch is given of the theory of electrolytic dissoideas.

ciation. This portion of the volume would have In recent years, Prof. Levi Civita has published a been improved by some concrete illustrations of the number of papers in the Atti dei Lincei dealing with methods of determining atomic weights. As it is, the particular solutions of the equations of dynamics, and reader must be very much at sea in understanding in especial with stationary motions. At the invitation what this constant actually means, apart from the imof Prof. Dickstein he has now prepared a simplified | plications of the atomic theory. account of these researches for the transactions of the The remainder of the book is occupied with an ** Prac matematyczno fizyczynych," published account of the properties and modes of preparation of Warsaw. The original starting point of the investi- each of the non-metallic elements and their chief comgation was the method of ignoration of coordinates, pounds. The history of each element is succinctly but the conclusions have now been shown to be results and well described, and important industrial applicaof a general principle applicable to any system of tions are also alluded to. There is an excellent account ordinary differential equations. They form a develop- of the modern manufacture of illuminating gas and ment of the work of Routh, and the stationary of acetylene, as well as of the commercial processes motions investigated by the author of Rigid Dy- adopted for the production of a number of the elements namics " are shown to belong to a particular class to and their compounds which find industrial uses. which Prof. Levi Civita gives the name of “ mouve- There is also a very complete account of the preparamenls å la Routh.".

G. H. B. tion and properties of the new gases of the atmosphere,

argon, &c., which, while interesting, does not throw

any new light on the obscure chemical relationships of A TREATISE ON CHEMISTRY.

these elements. In this connection the absence of an A Treatise on Chemistry. By Sir H. E. Roscoe,

account of the periodic classification under the general F.R.S., and C. Schorlemmer, F.R.S. Vol. i. The principles of the science is specially felt. It would Non-Metallic Elements. New edition, completely have been better to have included in the first part of revised by Sir H. E. Roscoe. Pp. xii +931. (Lon- this volume a complete consideration of the general don: Macmillan and Co., Ltd., 1905.) Price 215. principles of chemistry, including the determination of net.

atomic weights, instead of reserving the discussion of STR TIR HENRY ROSCOE is to be heartily congratu- the periodic classification and other matters of prin

lated by all chemists on the appearance of a ciple for the subsequent volume relating to the metals. new edition of the first volume of Roscoe and Schor- When the first edition of this volume appeared, many lemmer's " Treatise on Chemistry.” This volume of the lecture experiments described were new, and deals chiefiv with the non-metallic elements, and is were of interest and value to the teacher. A number now in its third edition.

of these are now generally familiar, whilst some of Many chemists remember the interest which the those still described have since been improved upon. first appearance of this volume excited in 1877. Printed This feature is indeed no longer a striking one in the in large, clear type, with excellent illustrations, it was book. Very few new lecture or laboratory experiments recognised both here and on the Continent as a clear are included. The teaching of chemistry is, however, and readable account of the facts relating to the no longer conducted on the old lines, and perhaps the chemistry of the non-metallic elements. If the student teacher would not now look to a treatise of this kind failed to find in it any new light on the obscurities of for this information. The fact that in some sections chemical theory, he at any rate was put in posses- of the work pains are taken to describe fully striking sion, not merely of the facts, but of the facts stated lecture experiments whilst in other and newer secwith a due regard for the history of their discovery tions this aspect is entirely neglected is a defect in the which was then and is still foreign to the ordinary general plan of the book which might be remedied in "handbook." There were, moreover, many experi

future editions. mental details of service to workers in the laboratory This raises the question as to the characters which recorded in the volume which were at that time not such a work as this should possess to be of real utility easily accessible to the ordinary student. During the at the present day. Handbooks and text-books of nearly thirty years which have elapsed since the first chemistry for the teacher abound, many of them exedition appeared, many treatises have been published cellent as practical guides to the work of the lecture in other languages, notably in German, but the trea- room and laboratory. Then there are more ambitious tis? of Roscoe and Schorlemmer still retains a certain works purporting to be of the nature of treatises. individuality for which it will be valued.

These, however, are too often ill-assorted and illIn preparing this edition Sir Henry Roscoe has had considered collections of the facts and theories of the valuable assistance of several collaborators with chemistry utterly lacking in those literary qualities special knowledge, and their handiwork is to some without which no work of the kind can expect to apextent evident in the different literary treatment which peal to the general reader or to take any permanent may be discerned in various sections of the book. place in the literature of the science. There is still

The first section of the volume relates to the general room for a treatise in the broad sense of the word, in principles of the science, including a description of the which the facts and doctrines of modern chemistr properties of gases and liquids, and a very intelligible expounded in a lucid manner free from the deti, account of the development of the atomic theory. A technicalities which are essential in a hanabu

text-book. Such a work should appeal to the teacher that " in the grasshoppers the front extremities have and to the student as a work of reference, and also to become a powerful leaping apparatus "; that an the outsider, it may be a worker in another department insect is covered with "dust" by the “ stigma" of science, who wishes to understand what the of a flower; that “if we take two beetles that seem science of chemistry now is without being confronted absolutely like each other and only differ in size " with all the bewildering and conflicting details of they are of different species; that “the frogs have the subject, such as the advanced student may find only one chamber to the heart "; and that “iron in Watts's Dictionary or in many German works on is always found combined with sulphur," it is diffichemistry.

cult to avoid the conclusion that the author has to Such a treatise, perfect as a broad and general answer for mistakes of his own. description and discussion of the science of chemistry, There are advantages in using the popular names has not yet been written in English. Roscoe and of natural objects in a book intended mainly for the Schorlemmer's treatise, however, still remains the unlearned. But a protest must be entered against nearest approach to the ideal.

the slovenly habit, too common with translators, of contenting themselves with a literal rendering of such

names into another language. How, for example. POPULAR EVOLUTIONARY THEORY,

is the English reader to identify the “ small nocturnal Darwinism and the Problems of Life; a Study of peacock's eye "'? If the scientific name be disallowed,

Familiar Animal Life. By Prof. Conrad Guenther. at least the recognised English popular title should
Translated by Joseph McCabe. Pp. 436. (London : be given.
A. Owen and Co., 1906.) Price 125, 6d. net.

Many of the author's conclusions on the main THIS 'HIS is a disappointing book. The idea of using subject are sound enough. It is the more to be re

the common sights and sounds of nature which gretted that his statements of fact are so often open are open to general observation as material for build- to adverse criticism, and that he has been, on the

F. A. D. ing up a detailed comprehension of evolutionary theory whole, so badly served by his translator. is a good one; there is much to be said for the inductive system of instruction as a supplement to the deductive methods more often employed. But in this

OUR BOOK SHELF. particular instance the errors in matters of fact are Aufnahme und Analyse von Wechselstromkurten, so prominent and so numerous as to overshadow By Dr. Ernst Orlich. Pp. viii + 117. (Brunswick such merit as the plan of the work possesses. Some F Vieweg and Son, 1906.) Price 3.50 marks. of these mistakes must be laid to the charge of the In the usual handbooks on alternating currents the translator, who obviously is but imperfectly acquainted methods of study of the wave-form of the alternations with the subject-matter of his original, and whose

and the analysis of the curves of E.M.F. and current want of due care appears in the occurrence of such

obtained are usually treated very scantily. Recently,

however, the subject has attracted considerable attenphrases as “the grouping of their elements is dif- tion, and its importance to a station engineer, who ferent from in dead albumen,” “ Pentastomum has wishes to make alternators not identical in design run little of the characteristics of a spider, to which it

well in parallel, is now recognised. really belongs,” and of such unwonted forms as

Prof. Orlich, of the Reichsanstalt, has endeavoured "terrestial," "adaption," "caracoid," "strepsitera”

in this little book to present a clear account of what

is known on the subject. It begins by definitions and --the last two being found more than once.

“ Sexu

a short mathematical introduction to the use of ally,” on p. 301, is clearly intended for “non- Fourier series, &c. Then follow descriptions of various sexually." "An example of a genius under the

methods of taking curves by the point-to-point progeneric title " is capable of easy emendation, but

cess, and of the apparatus of Rosa, of Callendar, and weel (p. 220) almost baffles conjecture. Can it of Hospitalier's “Ondographe.'

The Braun tube is described and illustrated, but no be meant for “ valve "?

mention is made of the fact that owing to the kathodeThe“ processionary butterfly

” is, of course,

ray bundle not being composed of rays of the same moth; the “ tentacles ” of the stag-beetle (p. 91) are magnetic deflectability, and the consequent lack of apparently its mandibles; we hear for the first time of sharpness of the moving image, its use for the study the bones of articulates, and that our muscles

of alternating currents is limited rather to qualitative

than to quantitative work. The next chapter deals are " secretory products.” It is implied on p. 143

with oscillographs in their various forms. Their theory that the adder is not poisonous. This is surprising is discussed, and the advantages of the different until we find from other passages that the author's patterns of moving needle and bifilar instruments “adder" is not an adder at all, but the harmless pointed out. ringed snake. A sentence on p. 226 is absolutely The recent experiments on telephony of Mr. Duddell.

and the wonderful curves shown by him at his recent unintelligible, unless we may conjecture that the word

lecture at the Royal Institution on the analysis and “ falls ” is an attempt to render the German “ Fälle,” transmission of sounds, show that substantial advances here obviously used in the sense of cases."

have recently been made in the construction of very It is charitable to the author to suppose that not sensitive oscillographs of his pattern, the curves of he but his translator is responsible for the statement

currents furnished by an ordinary microphone being that “in the case of moths and grasshoppers there

readily shown to a large audience.

After a chapter on the phenomena of resonance, the is not a very great difference in habits between the concluding portion of the book deals with the analysis larva and the imago.” But when we find it stated l of curves, with descriptions of the best-known forms



of harmonic analysers, including those of Henrici, and Chondromyces as special details. So far as one can the machine devised by Michelson and Stratton for their judge from these specimens, the drawing entrusted analysis of visibility curves of interference fringes. to Ehrlich, of Berlin, promises to combine correct

The information given in the book seems, on the representation and artistic treatment, and the pubwhole, fairly complete and accurate. The word “per- lisher's name is sufficient guarantee for good reproiode" seems used in a loose sense, sometimes as duction; the paper selected is not strong enough to ** time of a single oscillation" and sometimes as withstand wear and tear, but at a somewhat higher ** frequency.'

J. A. HARKER. price the plates may be obtained backed with linen Cultures du Midi de l'Algérie et de la Tunisie. By and attached to rollers. The size of the diagrams,

C. Rivière and H. Lecq. Pp. xii + 511. (Paris : about 5 feet by 3 feet, is sufficiently large for most J. B. Baillière et Fils, 1906.) Price 5 francs.

practical purposes. The short prospectus prefixed In view of the fact that inside the British Empire

to the accompanying text provides little information, agriculture is being practised under all sorts of except to say that the plates will be designed two, tropical and semi-tropical conditions, there is a

three, or more to each subject, that the series will singular paucity of books in the English language histories of plants, and that the lower plants will

cover the whole field of the anatomy and the lifedealing with the cultivation of exotic plants. The book before us, one of the “ Encyclopédie agricole

receive especially full treatment. series, reviews briefly the whole range of plants which | Reports of the Expedition to the Congo, 1903-5. are cultivated economically in the Mediterranean Liverpool School of Tropical Medicine, Memoir region belonging to France, i.e. in Provence, Algeria, xviii. Pp. 74. (London : Williams and Norgate.) and Tunis. This is a very special district possessing Price 7s. 6d. net. a characteristic flora adapted to its well-marked In this report, the late Mr. Dutton and Dr. Todd climatic conditions of insufficient rainfall which falls contribute an important paper on gland-palpation in mainly in the winter, great heat and dryness human trypanosomiasis, in which they show that in the summer, excessive radiation resulting in

most early cases of trypanosomiasis have enlarged extrene variations of temperature, with sharp frosts glands, and can therefore be detected by gland-palpain the winter, incessant wind, and an all-pervading tion. A second paper by the same authors discusses sun. ('nder these conditions many forms of agri- the distribution and spread of sleeping sickness in culture are only possible where irrigation water is the Congo Free State. This is illustrated by four obtainable, and much of the country is little better than maps, which demonstrate very clearly the enormous bare rock or sand; there are, however, many im. extent of territory in which this terrible disease is porlant cultures, special to the district, which have

now met with compared with twenty years ago. This been brought to a high state of perfection by the is in great measure accounted for by the increase inhabitants of the Côte d'Azur.

in travel following the opening up of the country. The most distinctive example is perhaps the growth Two new Dermanyssid Acarids from monkeys' lungs of plants for scent and essences which has its centre are described by Mr. Vewstead and Dr. Todd, and at Grasse, but which has been extended into both Dr. Stephens and Mr. Newstead contribute a paper on Ilgeria and Tunis; the rose, the orange-flower, the the anatomy of the proboscis of biting flies. It will tuber rose, the violet, and the jasmine being the most thus be seen that the report contains matter of conimportant of the flowers thus cultivated. The olive, siderable interest, and the general “get up leaves that most distinctive feature of all Mediterranean land- nothing to be desired. scapes, is losing ground, we learn, being displaced by Ten Years' Record of the Treatment of Cancer withthe competition of oils like cotton-seed and sesame;

out Operation. in Provence, also, the land is wanted for more in

By Dr. Robert Bell.

Pp. 107

(London : Dean and Son, Ltd., 1906.) Price 25. 6d. tensive forms of cultivation, such as the production of carly vegetables and cut flowers. The book of MM. Rivière and Lecq suffers some

It is difficult to understand the raison d'être of this what from the very extensive ground it has to cover;

book, which consists mainly of a diatribe against the the accounts of each plant in cultivation have to be

modern surgical treatment of cancer, and a veiled 20 curtailed that the details are insufficient for the

recommendation of the author's method of treatment needs of the practical man, who will, however, find by medicinal and hygienic measures. As regards any an excellent series of references to more special books | “record” of ten years' treatment by the author's and articles on each subject. The book may be of

methods we find little evidence--“ several cases considerable service to many of our colonists living in

eventually got quite well (p. 42), a case “ recovered semi-arid countries and looking round for suitable completely (p. 43), a case in which “the tumour and remunerative crops to grow; from it they can

quite disappeared (p. 63), three cases in which obtain both ideas as to possible introductions and recovery was complete (p. 71). This constitutes such economic information as to the labour required

the record ”; can the author be surprised if his and the probable value of the returns as may enable

view's and methods be received with scepticism? them to embark on the experiment with some prospect

R. T. H. of sucress.

The Opal Sea. By John C. Van Dyke. Pp. xvi + Tabulae Botanicae. (Part i., containing plates i. 262. (London : T: Werner Laurie, 1906.) Price and ii.) Edited by E. Baur and E. Jahn. (Berlin :

6s, net. Gebruder Borntraeger, n.d.) Price per plate : paper,

Prof. VAN DYKE provides in these pages a readable 7 mark; cloth, 10 marks. Series of five, 25 marks. account of many branches of modern oceanography USDER this title the publishers announce a series of expressed in a literary form too seldom found in works coloured illustrations of plants intended for lecture dealing with scientific subjects. Is one would expurposes, and arranged in sets for each subject, pect, the romance and postry of science are given order, or class. The two diagrams received illus- great prominence, and the attractive word-pictures

the Mycobacteriaceæ, the one representing reveal the fascinating nature of the work of the man -uccessive stages in the life-history of Polyangium of science. Many readers of these essays will be luneum, selected as a general type, the other depict- encouraged to undertake a more precise study of the ing the fructification, spores, &c., of Myxococcus and physical geography of the sea from formal treatises.





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Sir William White gives as the metacentric height a!

an actual submarine 37 feet when awash on an even [The Editor does not hold himself responsible for opinions keel, and only 45 per cent of this, say 16} feet, when

trimmed to an angle of 4 degrees. The value of vis expressed by his correspondents. Neither can he undertake

when l'= 10 knots, is about 9 feet, so that the effective to return, or to correspond with the writers of, rejected metacentric height would be reduced to about 28 feet on manuscripts intended for this or any other part of NATURE. an even keel, and to 7 feet when trimmed 4 degrees by

the stern. No notice is taken of anonymous communications.]

So far as can be judged from a diagram given

by Sir William White (Fig. 7 in his paper), the meta. The Stability of Submarines.

centric height would vanish altogether for a trim of

about 7 degrees. Sir William White, in his paper in the Roy. Soc. Pro- Thus a submarine moving ahead at to knots, even under ceedings (vol. lxxvii. A., p. 528), discusses the hydrostatic perfect conditions, might apparently be expected to founder forces tending to stability or instability of a submarine at if its inclination at any time reached as much as 7 degrees. the surface of the water. When the vessel is in motion, Sir William White mentions that in the case of the hydrodynamical forces come into play from the stream-line submarine A8, the hydrostatic metacentric height had been action of the water, and these also will affect the stability reduced, at the time the accident occurred, to 8 feet. of the vessel. Sir W. White insists that these forces can The further diminution in this height produced by a headonly be examined experimentally, and has no data to way of 8 knots is about 6 feet—by a headway of 9 knots give as to their magnitude. Although it is obviously im- is about 7) feet, leaving only about i foot of effective possible to obtain an exact calculation of the magnitude of metacentric height as the margin of safety. these hydrodynamical forces, yet it may be worth notic- Obviously these rough calculations ignore a great numing that a very simple calculation will give an approxi- ber of factors which ought to be taken into account before mation to their value, which at least is of importance in accurate knowledge can be obtained. The most important that it suggests that the question is one of extreme gravity. , of these factors is probably the proximity of the surface

The principle involved is, of course, the well-known and the consequent formation of surface-waves. A calprinciple by which an ellipsoid moving through still water

culation which omits a factor of this kind cannot lay tends to turn so that its smallest axis is in the direction claim to any value as advancing exact knowledge, but of motion.

may serve the humbler purpose of suggesting possible, and We may obtain a first approximation to the stream-line even probable, dangers, and of emphasising the need for action by treating the submarine as a cigar-shaped spheroid, experimental knowledge, before this is forced on us by a and assuming it to be completely immersed in an infinite catastrophe.

J. H. JEANS Let a, b denote the semi-axes of the spheroid, and Trinity College, Cambridge. let it be moving with velocity V, its major axis making a small angle A with the horizontal. The couple tending to decrease A is known to be

The mathematical investigation which Mr. Jeans puts B

forward is of great interest, but avowedly rests on the Vsin 20 \2-a

assumption of the complete immersion of a submarine in 2 - B

an infinite ocean. The concluding paragraph of his letter where

indicates that a great number of factors, which ought to

be taken into account, are not represented in the matheVas - 62 log

matical investigation, the most important being near 1(a? 62)

ala? 62,1

proximity to the surface and the consequent formation of

surface-waves. It will suffice, therefore, for me to say a - Va' - 72

that my insistence on the necessity for direct experiment, B=

log Ila-12) b 6492 - 62) / rather than mathematical investigation, had relation to the

case where the submarine was moving at the surface with and D is the displacement of the vessel.

a small reserve of buoyancy. The slides which I exhibited The figures given by Sir William White for an actual at the Royal Society reproduced photographs taken in these submarine are-length 150 feet, breadth 12.2 feet. If we

circumstances, and showed the singular and irregular take a b= 12.3 in our spheroid, we obtain

character of the surface-waves produced by the headway

of submarines under these conditions. These slides B

furnished conclusive evidence of the impossibility of re0'95. 2 B

presenting the conditions of practice by purely mathematical

investigation, and the absolute necessity for experiments on Thus, for a displacement rough a small angle a from models and full-sized submarines. the horizontal, the stream-line couple produced by a velocity Mr. Jeans's investigation for the completely submerged V through the water is

vessel has, however, a great practical value, because it

furnishes fresh and important reasons (in addition to those 0 95 V2 Do,

urged by myself) against the tendency to increase the

under-water speeds of submarines. When submerged, the tending to turn the vessel further from the horizontal. If h is the metacentric height for longitudinal displace- clination is found in the height of the centre of buoyancy

measure of stability of the vessel for all directions of in. ment, the hydrostatic righting couple is

above the centre of gravity. We are informed authori. ghD.

tatively that in the diving condition this height is less than

I foot in existing types of submarines. It will be seen, Thus the effective righting couple is

therefore, that a very small value of V-less than 6 knots --might render such a vessel unstable; if the speed were

increased to 10 knots no possible use of water-ballast could P

give such a hydrostatic stability to the vessel when at rest

as would secure the maintenance of stability when she so that the metacentric height is diminished by the motion moved at full speed. The existence of superstructures on of the submarine by an amount 0.95 V /g. This factor the upper portions of submarines, of course, involves a does not appear to depend much on the shape of the departure from the cigar-shaped spheroidal form, but carsubmarine; clearly, if its shape had been that of a thin not be accompanied by any such decrease in the moment long stick, we should merely have to replace 0.95 by 1.00, of the couple resulting from the stream-line forces as would whereas if the ratio alb had had only half of its present secure, or even add sensibly to, the safety of the submarine value, the numerical factor would still be about 0.9.

moving at high speed under water. W. H. WHITE.

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The Action of "a" Radiation on Diamonds. gravel into a collection of small puddles. The disturbance The action of the "a rays" on diamonds is of con

caused in each would be strictly confined to its own area, siderable interest, for while the fluorescence caused by the

and would be correspondingly intense within that area. B and y radiation from radium is probably similar to that

With a given stream of "a" radiation, a small stone caused by the X-rays, the appearance of a diamond made appears to give a very slight scintillating effect which is luminous by the impact of a stream of "a" particles

not seen in a larger stone, except at the edges and angles suggests some considerations as to the possible action of

of the facets, where the area of fluorescence is abruptly '" radiation on fluorescent crystals in general. The

terminated, and even here it is very faint. The above fluorescence of a fairly large stone (cut and polished) when

remarks would, of course, only apply to perfect crystals. viewed with a suitable lens shows practically nothing of

If a crystal is full of flaws and imperfections, the areas the spinthariscopic action, although the stone may be

or spheres of fuorescence would not find easy conduction brightly luminous. Instead of the familiar scintillations,

across the faults, and would therefore become localised in the whole crystal, or at least the whole surface exposed to

their action. It may be noted that a lump of willemite the rays, appears to give out a steady bluish-white light. (natural), which is of a semi-crystalline character, does The thought at once occurs to one that this seemingly

show scintillations, though very imperfectly, while the continuous flow may be the collective effect of the very

powdered mineral answers much better. This may be exnumerous scintillations produced by a too intense stream

plained on the assumption that the areas of conduction are

C. W. R. of "a" rays; such an action is well shown on a zinc

restricted to the size of the particles. sulphide screen when there is an excessive quantity of

June 20. radium used. That this action is really the collective fluorescence of scintillations is at once evident by removing

The Day of Week for any Date. the fragment of radium to a greater distance, reducing the quantity used, or increasing the magnifying power Tue following method for finding the day of the week employed to view the screen. In the case of a diamond, for any given date (new or Gregorian style) may interest however, this does not appear to be so. The use of a your readers. We assign a number for each month in higher power to view the fuorescence still shows a seem- accordance with the old style, beginning with March, so ingly steady glow, and the increase of the distance between that the last four months are numbered according to their the radium and the stone merely causes the light to be- Latin names, as follows :come gradually fainter, while still preserving its steady character. Yet it is certain that the diamond responds

January, o; February or March, 1; April, 2; May, 3; readily to the “a” particles, and also that, as the quantity June, 4; July, 5; August, 6; September, 7; October, 8; of radium is so very small, the action of the B and

November, 9; December, 10; next January, 11; next radiation is quite negligible. It is, of course, well known

February, 12. that when an "a" particle strikes a fluorescent screen, the

For a Leap Year, January and February must count as point of impact becomes the centre of a luminous area,

11 and 12 respectively in the preceding year. which is simply enormous in extent when compared with

It is only in dealing with the month-number that anythe size of the atomic projectile which causes it.

thing not straightforward and obvious is involved. The following may perhaps be suggested as a possible

The rule then runs as follows :explanation of this action :-When an particle strikes

A. For the century: divide by 4, and calculate 5 times a homogeneous fluorescent crystal (say a diamond), the the remainder. energy which excites the fluorescence finds equal conduction

B. For the year : add to the number the quotient obtained in all directions. The fluorescence caused thus tends to

from divisor 4. fill the whole volume of the crystal. If there are many C. For the month : multiply by 4, and negate the units such atomic projectiles incident on the same crystal, they digit (i.e. subtract instead of adding it). are all tending to do the same thing, and consequently D. For the day : retain the number unchanged. their spheres of influence mingle with one another. As such spheres of fluorescence find equal conduction of all

Then add together the results A, B, C, D (casting out sides, they extend indefinitely within the limits of the sevens, of course, as you proceed), and the result gives crystal in question. As fluorescence is apparently the required day of the week. molecular property, and probably electrical in its nature,

The rule holds without modification, not excepting such it is not difficult to imagine that such may be the case.

years as 1600, 2000, &c., as well as 1700, 1800, 1900, &c. A still pond, into which a handful of gravel is scattered, may present an approximate analogy. The ring-waves

Examples -1906, September 19. (neglecting the time they take to travel) would mingle with

A. For century : 3 x 5=15 one another, and yet each one might be said separately to

B. For year: 06+1=7 occupy the whole area of the pond. In the case of a zinc

C. For month : 4×7 gives 20 - 8=12

5 sulphide screen, or one coated with minute fragments of

D. For day:


5 diamond crystals, the energy received by one crystal or fragment of a crystal is confined exclusively to the volume

A+B+C+D=1154, i.e. Wednesday. of that fragment. Moreover, it is impossible for an “aparticle to strike more than one crystalline fragment at a

1815, June 18 (Battle of Waterloo). time, for it is a body of atomic dimensions compared with

A. For century: 2 x 5= 10

3 which the most minute fragment of the fluorescent compound would be enormous.

B. For year: 15+3=18
The whole of the available energy is thus confined to

C. For month : 4x4 gives 10 -6= 4
D. For day :

the limits of the fragment struck, and is not, apparently,
extended to the neighbouring crystals, which are only in

A+B+C+D=15--1, i.e. Sunday. loose and indifferent contact with it. When such a crystalline fragment is of a size which is comfortably visible 1784,* January 12 (Pitt's appearance as Prime Minister). with the aid of a lens magnifying about 20 diameters to zo diameters, the resulting fluorescence will be visible as

A. For century: 1 *5= 5 ...

5 a scintillation. To diminish the size of the crystals bevond

B. For piar: 83* + 20 = 103

-5 a certain point in order to increase the brightness of the

C. For month : 11* x 4 gives 40 - 4= 36 .
D. For day :

5 scintillations is apparently not advantageous, as it requires the higher powers of a compound microscope to render the

Leap year. areas properly visible, and there would be a corresponding loss of light.

A+B+C+D= 162, 1.t. Jouldır. On the analogy of the pond given above, the spinthari

1. E. scopic effect may be compared to throwing a handful of

King's College, Cambridge, July 11.



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