« PreviousContinue »
THURSDAY, MARCH 2, 1905.
Coulomb, Volt, Farad, Ampère, Ohm, Gauss, Maxwell and Henry, differs from the practical unit by
some power of 47. Yet the rational system is doubtA TEXT-BOOK OF ELECTROMAGNETISM. less an advantage from the point of view of pure Elements of Electromagnetic Theory. By S. J. theory, and would probably have been adopted in
Barnett, Ph.D. Pp. 480. (New York: The Mac- practice if only there had been someone to suggest millan Company; London: Macmillan and Co., it in the early days of the science. The student must Ltd., 1903.) Price 125, 6d. net.
remember that he is using the rational system when MODERN electromagnetic theory is so full of he compares the formulæ in this treatise with those interest, and yet at the same time so full of
in most other text-books. difficulties, that every fresh attempt to present an
The magnetic properties of currents are deduced elementary account of it in a systematic and con- from Ampère's result that the mechanical action nected form is sure to attract the attention of experienced by a circuit carrying a current I is the students who are endeavouring to gain a grasp of
same as it would experience if each element of length the fundamental principles of the subject. Such dL were acted on by a force IB sin 0.dL, where B students are always looking out for a good text- is the magnetic induction and a is the angle between book," hoping that this book, when found, will be dL and B; the direction of the force is at right better adapted to their needs than those they already angles to both dL and B. In this way the idea of possess. Their desire for something better probably the equivalent magnetic shell is avoided, and, in fact, arises, in part, from the difficulty of the subject, and we have found no mention of a magnetic shell in the the large number of new ideas which it presents to book. Yet the ideas which group themselves round their minds. It is perhaps too much to expect that a magnetic shell and the solid angle subtended by it a student should be able to gain from any single are of real assistance, and are not easily replaced: book really vivid physical conceptions of electric and The book, for the most part, goes over well worn magnetic phenomena and principles, for perhaps, ground, and thus the reviewer's attention is naturally after all, these can only gradually grow in the mind. directed more to the treatment of the various proposiThe author of the treatise under review has, it is tions than the propositions themselves. The clear, made a serious attempt to supply the student's treatment is generally fresh and vigorous, but in a want, so far, at least, as the more formal theory is few instances is hardly satisfactory. Taking the concerned.
electrostatic field due to a point-charge, the author The book is meant to give an introduction to the considers the equilibrium of a portion of the field subject, and thus the author does well to keep the bounded by an elementary circular cone and two conanalytical processes within the limits which centric spheres, and shows that the tension along the suitable for students whose mathematical attainments lines of force requires a pressure of equal amount do not go beyond some knowledge of the differential | at right angles to them. The result is extended to and integral calculus and of simple differential equa- the general case by the remark that “ since the field tions.
within the element of volume is uniform when the In the first part of the book, general electrostatic element is made indefinitely small, and since this is theory is treated in a fairly complete way, many true of any electric field, the result just obtained for problems being solved. The chapters on the con- a radial field holds universally." duction current, on electrolysis and on thermal and The attempt to establish a general result by the voltaic E.M.F.'s, which then follow, will be found consideration of a single special case is seldom satisuseful. The author next introduces magnetism, the factory. In the present instance the student would magnetic action of currents, electromagnetic induc- not fail to notice that the method which succeeds for tion and the magnetic effects of moving charges, and the non-uniform field within the conical element will concludes with a chapter on the transference of not apply if the tube of force is a circular cylinder electromagnetic energy
and electromagnetic so that the field within the element is really uniform. waves.
In chapter xiii. “ the coefficient of self induction Throughout the book the system of rational units (L) of a coil or circuit is defined to be the quotient originated by Mr. Oliver Heaviside is employed. On of the coil flux, N, due to the coil's own magnetic this system, if two unit charges are placed at unit field divided by the current I in the coil.” This is distance apart in a vacuum, each exerts a force of the way in which the coefficient is usually defined, 1/47 dynes upon the other. The adoption of this but it is an exceedingly unsatisfactory way, for unless system banishes the great 4* from many important the conductivity of the wire be infinite, lines of formulæ; for instance, on the rational system, the magnetic induction penetrate the wire, and then it magnetomotive force in any circuit is numerically becomes difficult to understand what is meant by the "qual to the total current linked with the circuit, and coil flux." It is impossible to escape from the the cnergy per unit volume in an electrostatic field difficulty by supposing the wire to become infinitely is fcE", where E is the electric force and c the thin, for the only result of this is to make L become specific inductive capacity. But though the 47 is infinite. driven from some formulæ it finds a refuge in others, Later in the chapter the coefficient of self induction with the result that every one of the rational units is defined by means of the expression (ILI?) for the corresponding to the practical units, i.e. to the energy of the system. 'It would be preferable to follow
Maxwell, and to adopt this definition at the outset, The subjects chosen are about equally distributed for it is from the value of the energy that the co- between those that are made at the telescope and efficient is always calculated.
those that have resulted from the discussion of the The methods of vector analysis are so useful in observations so made. This will be seen from a list electromagnetic theory and present so little difficulty of the several chapters or lectures (1) L'ranus and that the reader naturally expects to find them used in Eros, (2) discovery of Neptune, (3) Bradley's disa book which is intended to present a thoroughly coveries of aberration and nutation, (4) accidental modern introduction ” to that theory. The author discoveries, (5) the sun-spot period, and (ol the makes a slight use of this analysis in his later variation of latitude. Some subjects which might chapters, but in the case of vector products adopts have been expected to find a place, such as the disa hybrid notation. In the true vector analysis, as coveries resulting from the application of the spectroused by Heaviside, if the vector product of the two scope, have been omitted, but the list is sufficiently vectors A and B, which make an angle o with each varied, and we gratefully acknowledge having received other, be the vector c, the result is denoted by a considerable amount of pleasure from reading the C=VAB,
well-known and familiar tales, treated, as they are. while the magnitude (C) of the product is given by with the brightness and acuteness characteristic of C=AB sin 0.
The choice of the discovery of Uranus permits a In the author's notation the relation between c, and B is expressed by
well-deserved tribute to be paid to the memory of
the elder Herschel for the keenness, assiduity and C=VAB sin ,
patience which mark the work of that astronomer; the letter v serving to indicate that c is at right while the mention of Eros allows something to be angles to the plane of A and B. It is difficult to see said of the problem of the sun's distance and of the that this hybrid notation has any advantage over history of those times when the discovery of a small Heaviside's.
planet added something to the reputation of the lucky A few misprints have been noticed in a list sent discoverer. The Savilian professor has some amusout by the author; only a few others have been ing remarks on the subject of naming the host of detected.
small planets that diligence has added to our cataThe reader has probably already gathered from logues. He quotes the case of Victoria as giving this review that the treatise can hardly be described rise to an outcry by foreign astronomers, who objected as that “good text-book " for which the student to the name of a reigning sovereign being found in searches. Yet it is undoubtedly a useful book, and the list. But the real struggle of the purists was, with a little modification and revision would be one
we believe, over the christening of Fortuna, which of the best books of its class. The student who is Airy happily settled in favour of the discoverer's fortunate enough to have it at hand will often turn
choice, by aptly quoting the well known lines of to it with profit.
G. F. C. SEARLE.
Nullum numen habes si sit prudentia
Sed nos te facimus fortuna deam, cæloque locamus." ASTRONOMICAL LECTURES AT CHICAGO.
The second chapter or lecture is probably the least Astronomical Discovery. By Herbert Hall Turner, satisfactory in the book. The tale might have been
D.Sc., F.R.S., Savilian Professor of Astronomy in told without parading the old scandal of sixty years the University of Oxford. Pp. xi +225. With ago to such wearisome length. Controversy seems plates. (London : Edward Arnold, 1904.) Price out of place in lectures of this character. Prof. Turner IOS, 6d. net.
in reopening the old sore has apparently two objects, THE HE object of this book and the reason for its the one, the whitewashing of Airy, and the other. appearance are explained in a short preface. The the besmirching of Challis' reputation.
Very hard purpose
is to illustrate by the study of a few things are said of the latter to which we do not wish examples, chosen almost at random, the variety in to give further currency by repeating, but on the character of astronomical discoveries.” The words subject of Challis' lectures we doubt whether the “almost at random” seem a little out of place, for words given in Airy's “ Life" will bear the construcwe learn that the book comprises the matter that tion put upon them by Prof. Turner. There is no was originally delivered in a series of lectures to the evidence to show, or at least the author has not L'niversity students of Chicago, at the hospitable produced it, that Airy's opinion was different in 1844 invitation of President Harper. The expression is from what it was in 1834, when he wrote to the Rer. probably not to be taken too seriously. It is not T. J. Hussey: “I am sure it could not be done (prelikely that a distinguished astronomer, enjoying what dict the place of the disturbing planet) till the nature may be regarded as a cathedral position, would be of the irregularity was well determined from several careless in the preparation of his material. He successive revolutions " (of Uranus), p. 43. Airy, it would be anxious to give his best, both for the credit may be suggested, did not believe the problem soluble of English astronomy and for his own reputation. until he received Le Verrier's memoir in 1846. There is ample internal evidence, not only that the The account of Bradley's discoveries is excellent, lectures were carefully prepared, but also of judicious and the feature in it which will be especially valued selection.
is the brief history given of the Rev. James Pound,
Bradley's maternal uncle. The reputation of Pound in search of the eggs of the pearly nautilus. He found has been overshadowed by that of his more brilliant, these, but so much more of great interest, e.g. as to but perhaps less versatile, nephew, and it is most Peripatus, Amphioxus, Balanoglossus, Ctenoplana, desirable to give the uncle his proper position. The that his tenure of the Balfour scholarship was on two whole chapter constitutes a most delightful piece of successive occasions judiciously extended for a year biography.
beyond the allotted triennium. In his arduous but The accidental discovery of a new star does not well rewarded explorations, Dr. Willey was aided by differ materially from that of a planet, and the author the Government Grant Committee of the Royal admits that this fourth chapter might very well have Society, who may congratulate themselves on the fact been the first of the series, but we agree with him that the money at their disposal was never better spent that it is not a matter upon which to'lay any par- than on this enterprise. It has seldom been the happy ticular stress. The particular discovery is only a peg fortune of a single zoologist to bring together in a on which to hang the remarks that the author wishes short span such rich material, including some of the to make on certain subjects. In this case the dis- most interesting zoological types. covery of the new star " in Gemini, at Oxford, by In part i. Dr. Willey describes the structure and means of photography, serves to introduce an account development of Peripatus novae-britanniae, n.sp., and of the International Chart of the Heavens, and some in so doing throws some fresh light on the hetero. remarks connected with the behaviour of Nova Persei. geneity of the class Onychophora, which this This chapter presents a careful examination of the delightful creature." represents. Dr. Paul Mayer facts and suggestions that have been brought to light | describes a new caprellid; Mr. G. A. Boulenger disby observation. The history of Schwabe and his cusses a very rare sea-snake (Aipysurus annalatus) work on sun-spots do not call for any particular from the South Pacific; Mr. R. I. Pocock reports on remark. The chapter is not long, and it covers the the centipedes, millipedes, scorpions, Pedipalpi, and ground very satisfactorily. In the last lecture, Prof. spiders; and Dr. Sharp gives an account of the Turner gives an account of the variation of latitude, phasmids, with notes on their remarkable eggs. wherein he is scen quite at his best. The subject is In part ii. Prof. Hickson reports on Millepora, shownot so hackneyed as some of the other selections, ing that the single species (M. alcicornis) illustrates but to speak to Americans of the work accomplished that great variability in the form of growth which is by Mr. Chandler was, no doubt, inspiring, and the a characteristic feature of the genus. Prof. Jeffrey successive steps by which Mr. Chandler established Bell discusses the echinoderms (other than holohis case are described with clear, logical sequence. thurians, which are dealt with separately by Mr. F. P. Usually the author ends his lecture by pointing out Bedford). Mr. Arthur E. Shipley reports on the sipucuwhat particular lessons are to be drawn from the dis- loids, Mr. J. Stanley Gardiner on the solitary corals and covery under examination, and they generally amount
on the post-embryonic development of Cycloseris, Mr. to this, that there is no line of research, however Beddard on the earthworms, and Miss Isa L. Hiles on apparently unimportant or monotonous, which can be
the Gorgonacea, which includes some interesting new safely neglected. Some inquiries seem to offer a
species. more immediate prospect of success, such as the
In part iii. Dr. Gadow has an interesting essay on establishment of observatories in the Southern Hemi- orthogenetic variation in the shells of Chelonia, that sphere, to make accurate observations on the motion
is to say, cases in which the variations from the normal of the Pole; but at the same time unexpected dis- type seem to lie in the direct line of descent; Dr. coveries may lie in a direction precisely opposite to Willey describes three new species of Enteropneusta, that indicated by the most educated opinion at
and develops several theories, e.g. that the gill-slits present available. The conclusion may be obvious,
arose originally as perforations in the inter-annular but the remark is not unnecessary. To be led too
grooves for the aëration of the gonads which occupied strictly by authority is unwise, to neglect the teach
the dividing ranges; and Mr. A. E. Shipley reports ings of experience is a crime.
W. E. P.
on the echiurids, making a welcome attempt to revise the group and to determine its geographical range.
In part iv. Mr. Stanley Gardiner describes the strucZOOLOGICAL RESULTS.
ture of a supposed new species of Cænopsammia from Zoological Results based Material from New
Lifu, and comes inter alia to the striking conclusion Britain, New Guinea, Loyalty Islands and Else
that the so-called endoderm in Anthozoa, giving rise where, collected during the Years 1895, 1896, and to the muscular bands and generative organs, and 1897, by Arthur Willey, D.Sc. Lond. Parts i.-vi. performing also the excretory functions, is homologous Pp. vi+830; illustrated. (Cambridge: University with the mesoderm of Triploblastica. In terms of the Press.)
layer theory, of whatever value it may be, the actinoTHIS splendid series of zoological results" zoon polyp must be regarded as a triploblastic form.
should have been recognised at an earlier date Dr. Sharp reports on insects from New Britain, Mr. in our columns, but the six volumes have appeared L. A. Borradaile on Stomatopoda and Macrura from through a lustrum of five years, and the fine series of the South Seas, Mr. Walter E. Collinge on the slugs, memoirs has mounted up to a total which baffles re- | Mr. E. G. Philipps on the Polyzoa, Miss Laura Roscoe viewing.
As Balfour student of the University of Thornely on the hydroid zoophytes, and Mr. J. J. Cambridge, Arthur Willey went in 1894 to the Pacific Lister describes a remarkable type of a new family
of sponges. (Astroclera willeyana), a very interesting is given. The belief that one of its forms is identical novelty. Mr. W. P. Pycraft discusses the pterylo- with the Italian S. Calvescens must be abandoned if graphy of the Megapodii, Prof. Hickson and Miss Sig. Sommier's conclusion that this last plant is Isa L. Hiles the Stolonifera and Alcyonacea, and Dr.
S. Cineraria x S. erraticus, Bertolini, be accepted. It
is decidedly suggestive to find that our common Ashworth the Xeniidæ.
S. Jacobaea hybridises so much more readily with In part v. Mr. Arthur E. Shipley gives a description
an alien species than with its fellow Senecios of the of the Entozoa which Dr. Willey collected during his British Isles. Another curious fact concerning sojourn in the western Pacific, including Parocephalus hybrids deserves mention. The common cross Primula tortus, Shipley, a member of the interesting family veris x vulgaris, as found in Kenmure Park and in Linguatulidæ. Mr. R. C. Punnett discusses some several other localities, approaches very nearly to
the primrose, while the Ballinoscorney plant closely South Pacific nemertines, Mr. L. A. Borradaile has
resembles the cowslip. This curious state of affairs an interesting note on the young of the robber crab, demands experimental investigation. Space limitMiss Edith M. Pratt describes the structure of Neohelia ations forbid' mention of any more of the numerous porcellana, Mr. Boulenger reports on new blind points of general botanical interest contained in the snake from Lifu, and the Rev. T. R. R. Stebbing deals volume. with the Crustacea.
The author is to be congratulated on having proPart vi. contains Dr. Willey's contributions to the
duced something far more useful than the mere catanatural history of the pearly nautilus-a fine piece of logue of names and places sometimes dignified by the
County Flora." Particularly pleasing is the work—and his personal narrative, which is not less attention paid to local names, given in the Irish-Gaelic creditable. In his narrative, amid interesting details characters. It is rather surprising that philologists of how he went about his collecting business, he dis- do not devote more study to local and often rapidly cusses, as a zoologist, his new Peripatus, the Ascidian disappearing dialects. The botanist working 3 Styeloides eviscerans, which readily throws out its country district is exceptionally well placed for collectentrails in holothurian fashion, the interesting inter- advantage make use of his opportunities.
ing information on such subjects, and might with mediate type Ctenoplana, “ which no zoologist could encounter without experiencing a momentary thrill
Exercises in Practical Physiological Chemistry. By
(Camof satisfaction,” the lancelets and enteropneusts which
bridge: W. Heffer and Sons; London : Simpkin, he observed, some of the remarkable new forms which
Marshall and Co., Ltd., 1904.) Price 5s. net. he discovered, such as Astroclera, and the egg-laying Practical Exercises in Chemical Physiology and of nautilus_his main quest. The whole story reflects Histology. By H. B. Lacey and C. A. Panneti. great credit on the indefatigable explorer himself and B.Sc. Pp. 112. (Cambridge: W. Heffer and Sons; on those who have assisted him in working up the London : Simpkin, Marshall and Co., Ltd., 1904
Price 2s, net. descriptions which form this imposing six-volume series of zoological results.
Nothing more forcibly illustrates the growing importance attached to the chemical side of physiology than the institution of practical courses dealing with
this branch of the subject in centres of physiological OUR BOOK SHELF.
teaching Accompanying this is a multiplication of Flora of the County Dublin. By Nathaniel Colgan. practical guides. Every teacher has his idiosyncrasies
Pp. lxx+324. (Dublin : Hodges, Figgis and Co., in the exercises he selects for his classes, but one is Ltd., 1904.)
inclined to doubt whether these are always sufficiently
pronounced or important to justify him in issuing a In many respects this district is an interesting one, and the floral distribution not quite what might have despised, and will in the end lead to the survival of
fresh handbook. Competition, however, is not to be been expected from a consideration of the adjacent the fittest. In the struggle, Mr. Cole's little book. counties. The flora resembles that of southern rather which represents the Cambridge course, will doubtthan northern Britain, but the somewhat unexpected less maintain its own. Though short it is admirably result is arrived at that the western Irish flora has clear, and the practical exercises are judicioush a considerably larger proportion of northern plants selected. The author is well known for his researches than has the corresponding eastern flora. The book in physiological chemistry, and possesses that pre opens with a summary of previous work in the dis- liminary knowledge of pure chemistry which is so trict from the fifteenth century to the present day. necessary nowadays for a successful pursuit of its The physical features are then described, and a section physiological application. headed“ Relations of Plants and Soils " lays par- The book is free from illustrations; the student is ticular emphasis on the distinction between “calci- required to make his own drawings of crystals. fuges” and “calcicoles."
absorption spectra, and so forth in the blanks left Some plants curiously absent from the county are for the purpose. This is an admirable idea, and our mentioned, one of which, Nymphaea alba, L., occurs hopes that the zealous and interested care that Mr in Meath, Kildare, and Wicklow. Both Trifolium Cole asks from the students in his preface will be repens, L., and T. dubium, Sibth., are stated to do responded to in the manner he desires. duty as the shamrock or shamrogue. Probably Oxalis The book does not pretend to be complete, but acetosella, L., has never served as the Irish national an elementary introduction to more advanced work it badge, this erroneous impression apparently dating is excellent. I do not propose to direct attention from a paper by J. E. Bicheno published in 1830. Mr. faults of omission, for these are obviously intentional. Colgan cannot add Epilobium tetragonum, L., to the the only fault of commission I have discovered is an Irish list, although E. obscurum, Schreber, is common p. 78, where the statement made implies that in the upland districts. A description of that interest: potassium ferricyanide contains oxygen. ing hybrid Senecio Cineraria, D.C., x S. Jacobaea, L., The second book, that by Messrs. Lacey and
Pannett, demonstrates that practical classes in
LETTERS TO THE EDITOR. physiology are not confined to universities and colleges of university standard. The book itself is (The Editor does not hold himself responsible for opinions not a serious contribution to scientific literature, and
expressed by his correspondents. Neither can he undertake
to return, or to correspond with the writers of, rejected its authors have neither the requisite training nor manuscripts intended for this or any other part of NATURE. knowledge to make it such. It is a mere compilation No notice is taken of anonymous communications.) or rechauffé from other well known text-books. One notes that one of the authors blazons upon the title
Charge carried by the a Rays from Radium. page that he has obtained a scholarship, at the No special difficulty has been experienced in showing that inter. M.B. examination at the University of London, the B particles (electrons), expelled fronı radium, carry with and this is a fair index of what the reader may them a negative charge of electricity. The positive charge expect in the interior of the volume. A note-book left behind on the vessel containing the radio-active material carefully kept by any moderately good medical student
is simply and strikingly illustrated in the arrangement dewould be equally worthy of publication.
vised by Strutt, which is now popularly known as the
"radium clock." W. D. H.
Since the a particles are deflected by a magnet as if they
carried a positive charge, it is to be expected that this Laboratory Notes on Practical Metallurgy: being a
charge should be easily detected; but all the initial experiGraduated Series of Exercises. Arranged by Walter ments made for this purpose resulted in failure. Since there Macfarlane, F.I.C. Pp. x+ 140. (London : Long- are four products in radium which give out a particles, and
mans, Green and Co., 1905.) Price 25. 60. only one which gives out B particles, it is theoretically to This little book is apparently intended as a first
be expected that four a particles should be expelled from
radium for each B particle. course for beginners in practical work in a metallurgical laboratory, and especially for those who are p. 212, 1904) I described some experiments that were made
In the Bakerian lecture (Phil. Trans., series A, vol. cciv., preparing for the examination of the Board of
to determine the charge carried by the a particles. About Education in stages 1 and 2 of practical metallurgy, half a milligram of radium bromide was dissolved in water, For these classes of students it will be useful and and spread uniformly over a metal plate and evaporated to deserves commendation.
dryness. With a plate of 20 sq. cm. in area, the absorpIt consists of a series of practical exercises, all tion of the a rays in the thin film of radium bromide is well within the grasp of the average boy, graduated negligible. The solution of the radium released the emanaand arranged with the view of developing the habit tion, and several hours after removal, the activity of the of observation, and the instructions given for doing the B and y rays from it practically disappeared. The exthem show a much more intimate acquaintance with periments were made with the radium film at this minithe simpler operations of a metallurgical laboratory
mum activity, in order to avoid the complication which than is generally found in works of this class. In would ensue if the B particles were present. An insulated the first eighteen pages the student is introduced to plate was placed parallel to the radium plate and about furnace work by simple experiments on the melting 3mm. away from it. The apparatus was enclosed in an of metals under various conditions, to prepare him air-tight vessel, which was exhausted to a very low vacuum. for the subsequent more difficult operations.
The current between the plates was measured by an electroThe preparation of the ordinary common alloys meter. The saturation current between the plates rapidly ollows, and then a series of well-chosen exercises fell with decrease of pressure, but soon reached a limiting illustrates the oxidation of metals and the reduction
value-about 1! 1000 of the initial--which could not be reof metallic oxides and sulphides. Later, the more
duced further, however good a vacuum was obtained. No complex subject of the principles on which the pro could be obtained. It was thought possible that the in
certain evidence that the a particles carried a positive charge cesses for the extraction of copper, lead, gold, and ability to reduce the current below this value might be silver from their ores depend is dealt with.
due to a strong secondary radiation, consisting of slowThe book concludes with a few elementary exercises moving electrons, which were liberated by the impact of the in assaying gold and silver ores, and the analysis of a particles on matter. Strutt (Phil. Mag., August, 1904) coal and coke. In the appendix are several tables, has also observed a very similar effect, using a plate of the most important being one giving the percentage radio-tellurium, which is well suited for this purpose, as it composition of some of the common alloys.
gives out only a rays. There are a few slips and blemishes in the text,
J. J. Thomson (Proc. Camb. Phil. Soc., November 14, but they are for the most part trivial, one of the
1904 ; see NATURE, December 15) has recently shown in a chief being in the table just mentioned, in which striking manner that a large number of slow-moving elec
trons are liberated from a plate of radio-tellurium, although the composition of the British gold coinage is given this substance is supposed to emit only a particles. These as gold 91.66, silver 8.33; the latter should of course electrons could be readily bent back to the plate from which be * copper." The book contains much useful in they came by the action of a magnetic field. No indication, formation for junior students, and can be recom
however, that the a particles carried a charge was mended for their use.
I have recently attacked this problem again, using the Le Liège. Ses produits et ses sous-produits. By M. methods and apparatus previously described, but, in addi
remove the Martignat. Pp. 158. (Paris : Gauthier-Villars and tion, employing a strong magnetic field to
slow-moving electrons present with the a particles. The Masson et Cie.) Price 2.50 francs.
apparatus was placed between the pole-pieces of an electroThe latest addition to the “ Encyclopédie Scientifique magnet
, so that the field was parallel to the plane of the des Aide-Mémoire ” is divided into two parts. The plates. In such a case, most of the escaping electrons defirst part is concerned with the formation of cork in scribe curved paths and return to the plate from which they Quercus suber, the distribution of the tree, its treat
set out. On application of the magnetic field, a very striking ment, its maladies and enemies, &c., and concludes alteration was observed in the magnitude of the current. with an account of prices and other commercial con
The positive and negative currents for a given voltage were siderations. The second part describes how the natural
greatly reduced. The upper plate, into which the a parproduct is treated in the manufacture of corks of good vacuum, this was the case whether the lower plate
ticles were fired, rapidly gained a positive charge. In a all kinds, and how it is utilised in the production of was charged positively, or negatively, or connected to earth. linoleum and other materials.
The magnitude of the charge, deduced from these experi