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ARMY EXAMINATIONS, CAMBRIDGE HIGHER LOCAL, &c., &c. For detailed Prospectus and List of Successes, apply to the SECRETARY of the Physics Classes. UNIVERSITY COLLEGE, DUNDEE. PRINCIPAL-W. PETERSON, M.A. Edin. and Oxon., LL.D. St. Andrews. The Systematic Instruction given in the above Subjects is such as is required for the Matriculation and Intermediate Examinations in Arts and Science of the University of London; for the Degrees of B.Sc. and D.Sc. of the University of St. Andrews; for two of the three years of Study required for graduation in Science in the University of Edinburgh; and for the L L.A. Certificate for Women. The Laboratories of the College, and of the Technical Institute in connection therewith, afford every facility for instruction in Chemistry (including Dyeing and Bleaching), Applied Mechanics, Physics, Engineering (Mechanical and Civil), Applied Electricity, and Drawing. MEDICAL DEPARTMENT. -The recessary Instruction is provided in the Subjects required for the various Medical Preliminary Examinations. The Systematic and Practical Classes in Chemistry, Biology, and Botany are already recognized by the University of Edinburgh; and by means of these Classes, along with Practical Anatomy and Hospital Practice, Students may complete two Anni Medici. SHIELL & SMALL, Secretaries. ST. GEORGE'S HALL, LANGHAM PLACE. The opening Lecture next Sunday afternoon (October 21), at 4 o'clock precisely, will be by WM. LANT CARPENTER, Esq., B.A, B.Sc., on Electric Lighting its Present Position and Prospects" (with Oxy-hydrogen Lantern Illustrations and Experiments). Members' Annual Subscription, £1. due October 1. Tickets for this series (one for each Lecture) to the SIXPENNY SEATS now reduced to 15. 6d. For Tickets and Lists of the published Lectures apply, by letter, inclosing Remittance, to the Hon. Treasurer, WM. HENRY DOMVILLE, Esq., 15 Gloucester Crescent, Hyde Park, W. Payment at the Door.-Admission: One Shilling (Reserved Seats), Sixpence, and One Penny. LIVING SPECIMENS FOR THE MICROSCOP GOLD MEDAL awarded at the FISHERIES EXHIBITION THOMAS BOLTON, 83 CAMDEN STREET, BIRMINGER Who last week sent to his subscribers Fredericella sultana, with sket. descr.ption. He also sent out Volvox globator, Pedalion mira, Craz mucedo, Alcyonella fungosa. Paludicella Ehrenbergi, Plumatella, Brach pala. Melicerta ringens, Stephanoceros; also Amoeba, Hydra, Van Crayfish, and other Specimens for Biological Laboratory work. Weekly announcements will be made in this place of Organisms ↑ is supplying. Specimen Tube, One Shilling, post free. Twenty-six Tubes in Course of Six Months for Subscription et [: or Twelve Tubes for 10s. 6d. Portfolio of Drawings, Eleven Parts, 15. each. An ASSOC. ROYAL SCH. MINES (Nor Sch. Sc.) is very desirous of obtaining an Immediate Engagen: any capacity, Scientific much preferred; Scholarship holder at N many Certificates from South Kensington and elsewhere; some a ance with French, German, and Spanish.-Apply G. W. C Fentiman Road, Clapham Road, London, S. W. KING'S COLLEGE, LONDON. BACTERIOLOGICAL LABORATORY. The WINTER COURSE commences NOVEMBER 1. Practical Instruction, under the personal superintendence o CROOKSHANK, is given daily, from 10 a.m. to 4 p.m., except Sa when the Laboratory is closed at 1 p.m. Lectures during November daily, except Saturday, from 12 p.m. to 1 Fees:-For the whole Course, £5 5s.; for the Lectures and Demonstra £3 35. J. W. CUNNINGHAM, Secretar AUTUMN TOUR IN THE MEDITERRANEA The Orient Company will despatch their large full-powered steat Garonne, 3876 tons register, 3000 horse-power, from Tilbury Docks, L on November 15, for a five weeks' cruise, visiting Lisbon, Tangier, Güre Algiers, Palermo. Naples, Leghorn, Genoa, Nice (for Riviera), Manja arriving in London on December 22. The Garonne is fitted with the electric light, hot and cold baths Cuisine of the highest order. Number of passengers strictly limited An experienced surgeon will be carried. Managers:-F. Green & Co., Anderson, Anderson & Co., } Fenchurch Avenue, E.C For terms and other particulars apply to the latter firm, or to the End Agents, Grindlay & Co., 55 Parliament Street, S.W. TO STUDENTS.-One or Two Student offered good BOARD AND RESIDENCE in lady's superior ha Ten minutes from Science Schools, &c. Apartments if prese Bath.-Mrs. A., 75 Finborough Road, South Kensington. GILCHRIST LANTERNS FOR CHEMICAL & ELECTRICAL EXPERIMENT As used by WM. LANT CARPENTER, Esq., B A., and Prof. FORIES, P Trade Hall, Manchester, before 5000 people. HUGHES'S PATENT ROTARY TRIPLE Center* Optical Lantern for Electric or Limelight, fitted with a new form of p Oxyhydrogen MICROSCOPE with Highest-class Objectives, d Eye of Fly 18 feet in diameter. The GILCHRIST Lantern for PHYSICAL EXPERIMENTS and SPECTROSCOPE Work, and OPTICAL LANTERN Diagrams, &c. This magnificent Instrument will give perfect definition. Suitable for Colleges and School Demonstration. MICROSCOPE ATTACHMENT for adapting to any Lae New Pattern. £7 158. DIRECT NICOL PRISM POLARISCOPE. PATENT PAMPHENGOS gives 12-feet Pictures. B. J. Mank Esq., compares it to the Limelight. £2 105. The DOCWRA TRIPLE. Finest Instrument in the World. E Medal. Highest Award, Photographic Exhibition. BIUNIALS. Elegant Brass Fronts, complete Outfits, Gas-bar. £15 155. 60,000 Slides, 300 Lecture Sets, Science Lectures, &c. Ch and Best for High-class Work. Illustrated Catalogue, 300 pages Postage, 3d.; ditto Pamphlets, 3d W. C. HUGHES, Patentee, Inventor, and Specialist, BREWSTER HOUSE, MORTIMER ROAD, KINGSLAND, LONDON, 1 Inventor of the Giant Aphengescope, Optical and Physical Apparata of the Highest Class. THURSDAY, OCTOBER 18, 1888. NATURE APPLICATIONS OF DYNAMICS TO PHYSICS AND CHEMISTRY. Applications of Dynamics to Physics and Chemistry. By J. J. Thomson, M.A., F.R.S., Cavendish Professor of Experimental Physics, Cambridge. (London : Macmillan and Co., 1888.) HIS is one of the most original books on mathe 585 state of the body if we had the power of noting every detail of its molecular structure. Using theorems due to Thomson and Tait and to Larmor respectively, Prof. J. J. Thomson shows that the second difficulty may be overcome if the co-ordinates of the values of which we are ignorant do not enter into the expressions for the kinetic energy of the system. It then, however, becomes necessary to modify the Lagrangian function, but this new form is such that when it is expressed in terms of any variable quantities and their "velocities" they satisfy the mathematical condition to which true geometrical co-ordinate and velocity are Tematical physics which has appeared for a long suhiera u to the modified Lagrangian function, and e time. Prof. J. J. Thomson has elaborated a method of very wide scope, and has applied it to a large number of problems of very different kinds. A reader of the work must perforce be struck not only with the mathematical ability of the author, but with the wide extent of learning which enables him to illustrate his theme by recent researches in nearly every branch of physics and physical chemistry. The method employed is so essentially mathematical that it is not easy to describe it without the use of symbols. As, however, it is a matter of considerable importance that those who are studying by means of experiment the phenomena discussed by Prof. Thomson should have some idea as to the progress already made in their theoretical explanation, it may be well to give an account of the general principles which he has used. In ordinary dynamics it is necessary to specify the positions of the members of a system of bodies of which the movements or mutual actions are under consideration. This is done by means of co-ordinates, which define their positions at a given time with respect to certain given lines or surfaces. If the system is in motion, the values of these quantities change with the time, and thus the co-ordinates may be regarded as possessing velocities. The difference between the kinetic and potential energies of the system (which is called the Lagrangian function) can be expressed in terms of the co-ordinates and their velocities, and if this is done the magnitude of the force which is acting on the system and tending to ncrease the value of any particular co-ordinate can be deduced from it. If no such force is acting, it follows hat a certain relation between the co-ordinates and their velocities must be satisfied. This is a perfectly general dynamical method, which could be directly applied to the complex system of atoms and ether by which the physical phenomena displayed by any given body are produced, if it were not for lifficulties which Prof. Thomson has attempted, as far as n ay be, to overcome. In the first place, the dynamical method presupposes knowledge of the relative positions of the members of he system, i.c. of its geometry, and we cannot at present x press "such things as the distributions of electricity nd magnetism, for example," in terms of the relative ositions or movements of atoms and ether. In the next place, even when we can express certain hysical states in terms of quantities which completely escribe all that we can observe, it is certain that in eneral they would not suffice to describe completely the VOL. XXXVIII.—No. 990. The term co-ordinate is thus used by Prof. Thomson in of its velocity the modified Lagrangian function can be the generalized sense of any quantity in terms of which and expressed, and he assumes that as far as the phenomena under consideration are concerned the state of a body may be described by four different types of co-ordinates. These specify (1) the position in space of any bodies of finite size which may be in the system; (2) the strains in the system; (3) its electrical, and (4) its magnetic state. The most general expression for the Lagrangian function is then formed. It may contain terms of various kinds. Prof. Thomson goes through them one by one, determines what the physical consequences of the existence of each would be, and if these are found to be contrary to experience concludes that the term in question does not exist. A similar method is applied to the coefficients of the terms which are shown to be possible. Thus a term exists which contains the squares of the velocities of the It corresponds to the expresgeometrical co-ordinates. sion for the ordinary kinetic energy. Prof. Thomson inquires whether the kinetic energy depends only on the geometrical co-ordinates, or whether it also varies with the electrical state of the various members of the system. The answer is given by means of an investigation of his own (Phil. Mag., April 1881), in which he has shown that the kinetic energy of a small sphere, of mass m, and with a velocity v, isradius a, charged with e units of electricity, and moving electrification should be recognized, as it follows that the speed with which electrical oscillations are propagated across any medium will be diminished by the presence of conductors moving about in it. "Thus, if the electromagnetic theory of light is true, the result we have been discussing has an important bearing on the effect of the molecules of matter on the rate of propagation of light." It would take too long to follow the author in detail through the interesting discussion which is pursued on these lines. Another example must therefore suffice. The specific inductive capacity of a dielectric depends upon the strain, and it follows that the distribution of stress which Maxwell supposes to exist in the electric field is supplemented by another, which is due to the relation between inductive capacity and strain. Maxwell's distribution will be the same for all dielectrics, but Quincke has shown that though most dielectrics expand when placed in an electric field, the fatty oils contract. In these cases the effects of what may be called the supplementary distribution are contrary to, and greater than, those produced by Maxwell's stress. Phenomena which depend on temperature are specially discussed, and an interesting conclusion with respect to thermo-electricity may be noted. It is that from the heat developed by a current at a junction of two dissimilar metals we can derive information as to that part only of the electromotive force which depends upon the temperature. Hence the Peltier effect can throw no light upon the absolute difference of potential between two different metals. A chapter is devoted to the calculation of "the Lagrangian function in the simplest case, when the body is in a steady state, when it is free from all strain except that inseparable from the body at the temperature we are considering, and when it is neither electrified nor magnetized." Two forms are found, which hold for the gaseous and the liquid or solid states respectively. The general principle is also laid down, that, "when the physical environment of a system is slightly changed, and the consequent change in the mean Lagrangian function increases as any physical process goes on, then this process will have to go on further in the changed system before equilibrium is reached than in the unchanged one, while if the change in the mean Lagrangian function diminishes as the process goes on it will not have to proceed so far.” As an example of this we may take the effect of a charge of electricity on the vapour-pressure of a liquid. If a spherical drop, of radius a, surrounded by a medium of specific inductive capacity K, is charged with e units of electricity, its potential energy is increased by e2 2Ka, and thus electrification changes the mean Lagrangian function by the amount -e2Ka. Prof. Thomson quotes experiments by Blake to prove that when an electrified liquid evaporates the vapour is not electrified, so that the charge e is unaffected by evaporation, while the radius a of course diminishes. On the whole, then, evaporation algebraically diminishes the terme2 2Ka, and therefore it will not proceed so far as before the liquid was electrified. Thus electrification diminishes the vapour-tension by an amount which is limited by the insulating power of the air. The maximum effect is about equal in magnitude, though opposite in sign, to that due to a curvature of a quarter of a centimetre. The suggestion is made that we should therefore expect an electrified drop of rain to be larger than an unelectrified one, so that this effect may help to produce the large drops of rain which fall in thunderstorms. The principle also leads to the conclusion that the density of saturated aqueous vapour in the presence of air is greater than if no other gas is present, and thus, apart from other causes, rain-drops would form more easily when the barometer is failing than when it is rising. The properties of dilute solutions are discussed at length, and the Lagrangian function is calculated in accordance with the views of Van 't Hoff on the assump tion that the molecules of a salt in a dilute solution behave as though they were in the gaseous state. The results obtained cannot be considered favourab to the view that the effects of solution are capable ci being stated in such simple terms. Röntgen ard Schneider's experiments on the compressibility of saline solutions prove that the decrease in the compressibility is sometimes more than a hundred times greater than that calculated on the above assumptions. The author also points out that the rise in the osmometer, which explained as due to the pressure of the dissolved salt, may be capable of other interpretations, and that at preser: the indications of the instrument must be considered ambiguous. Enough has perhaps been said to give an idea of the method and scope of Prof. J. J. Thomson's work. It is possible that some of the experimental results which are quoted require fuller confirmation than the have as yet received, but if the work is regarded as a text-book of mathematical physics this is a very ming defect. The author has developed a method of w scope, and it is important that its applications should be fully illustrated, even if the data assumed are not in a cases unexceptionable. The book literally bristles with novel suggestions are points of interest. An explanation of the fact recent). discovered by Mr. Shelford Bidwell, that iron become shorter when the magnetizing force is very great; the effect of surface-tension on electromotive force; chem. action in thin films; the effect of a neutral gas on disseca tion-these are some of the subjects, in addition to the which have already been mentioned, upon which we on turning over the pages haphazard. That it will make the study of physics and chemistr easier is only in one sense true. Nihil tetigit quod ornavit may, as applied to Prof. J. J. Thomson, be free translated, that he hardly mentions any law of physic except to complicate it with correction terms. From a more serious point of view, however, difficult to over-estimate the value of the establishment the less obvious connections between phenomena. On many points, such as Quincke's and Bidwell's obser vations on the changes of magnitude produced in electric and magnetic fields respectively, experime needed the support of theory, and Prof. J. J. Thoms points out causes to which the observed effects may due. Almost daily, conscientious experimentalists 3 spending time and ability in the detailed examination facts which they cannot explain, and which they can hope to explain by the most minute investigations. It ises just mentioned the labour was well spent, but in hers it is practically thrown away in the attempt to erce a labyrinth the clue to which can be found only by athematics. Prof. J. J. Thomson's book ought to be trefully studied by all physicists, and especially investiitors who have discovered what they believe to be a new ct. In many cases it will suggest possible explanations hich may prevent long and wearisome groping in the ark. The author is to be warmly congratulated on his work, hich is an achievement of a high order, and which will id to his already great reputation as a mathematical hysicist. RECENT WORKS ON ORNITHOLOGY. rgentine Ornithology. By P. L. Sclater, M.A., F.R.S., R. SCLATER AND MR. HUDSON have combined One of the most interesting features of the work will btless be the introduction, which will appear in the cond volume, when it will be possible to form some curate notion of the relations of the avifauna of the gentine Republic with that of the neighbouring States, comparison which will doubtless be of importance to naturalists who are interested in the somewhat comcated natural areas of the neotropical region. At also on the success with which he has contrived to attach an English name to each bird. Everyone who has tried to do this, when writing on exotic birds, knows how difficult it is to invent English titles for species which have no counterpart in European nomenclature ; and we must acknowledge that the names are a great improvement on some of the zoology "as she is taught " at our Zoological Gardens. Should some of the names bestowed upon animals in the “Zoo” ever be adopted in general works of travel, we might expect to find such truthful anecdotes as the following: "The insolent behaviour of one of the animals considerably annoyed us, from its persistent habit of making 'long noses' at us. On shooting a specimen we discovered that it was a Rude Fox (Canis rudis)," &c., &c. "Some interesting little creatures now came in sight, dancing, apparently in perfect time, across the glade. They proved to be Pleasant Antelopes (Tragelaphus gratus)," &c., &c. "Just as I was emerging from a thicket I managed to trip over something which brought me heavily to the ground. I fancied that I had fallen over a tree-stump, but on careful examination, it proved to be an Inconvenient Curassow (Crax incommoda) which had somehow got in my way," &c., &c. In his useful little work, a "Key List to British Birds," Colonel Irby has supplied a real want-a handy pocketbook, giving just the diagnostic characters of every species. It is a desirable supplement to the "List of British Birds" published by the British Ornithologists' Union, which dealt with the nomenclature of the various species, but which might also with advantage have contained diagnoses, such as Colonel Irby's industry has now supplied. What Colonel Irby has done for the birds, Mr. Miller Christy does for the eggs of British birds, and it is certain that with this little work in his hands the young student can gain a very good idea of the eggs which are likely to be met with in England. The call for this second edition of the late Mr. Newman's work shows apparently that notwithstanding the prohibitions of an Act of Parliament; there are a good many egg-collectors in this country, nor can we state with truth that there is any falling off in the number of students of the egg-collection in the British Museum since the Wild Birds Preservation Act became law. To the chapter on bird-skinning we would add a practical hint that before commencing operations a tiny wisp of wool should be inserted into the palate of the specimen. This greatly prevents the risk of discharge from the nostrils, and saves many a skin from being draggled and sent the genera and species peculiar to the region spoilt. The American method of enveloping the prepared ated of by the authors seem to be few in number, and y would appear to be limited to the more western tions of the country, especially the district of Tucuman. t would be easy to give many extracts from Mr. dson's charming writings on the habits of the birds, h the life-history of many of which he is as familiar as are in England with that of many of our British birds, ile his travels have enabled him in many instances to e an account of species both in their summer and ter homes. To any naturalist visiting Argentina this k will be of the highest value, the descriptions given Dr. Sclater being short and concise, but sufficient for identification of species, while he is to be congratulated skin in wadding is also far preferable to our method of fastening a paper band round the specimen. papers of various kinds. The author's language is very inexact if compared with the language of Thomson and Tait's "Natural Philosophy," or Dr. Lodge's text-book. It reads as if a shorthand-writer had taken notes of lectures, and the lecturer had published them after hasty correction. This inexactness is visible in almost every definition in the book. We read of velocities acting and accelerations working. New magnitudes are introduced; thus, "the intensity of a force is like the temperature of a body. It is measured by the velocity communicated, apart altogether from the mass to which it is communicated." "But the quantity of a force is like the amount of heat in a body. Force-quantity is measured by the product of the velocity communicated and the mass to which it is communicated" (p. 103). In defining, if he can be said to define, "impressed force," the author uses expressions such as so that when we speak or read of an accelerating force, for g, or 98 or 32'2, or a per second per second." This book would certainly not be recommended by us to any student who is desirous of obtaining a knowledge of mechanics; but, for all we know, it may very well serve the purpose for which its author has designed it. It is a book written for candidates in certain examinations by a successful candidate. The author has introduced side lines to catch a student's eye, and we think this a very clever contrivance. Thus there is the side line "Pressure" (p. 2), and the student is directed to get off by memory: "When a body is prevented from falling towards the earth by the hand or by a table, e.g., the body exerts a certain pressure upon the hand or the table." It is interesting to know from such an authority as Dr. Aveling that this is the sort of definition which satisfies an examiner, and it seems to us that a study of this book by examiners would lead to very useful results. Solutions of the Examples in an Elementary Treatise on Conic Sections. By Charles Smith, M.A. (London: Macmillan, 1888.) 66 MR. SMITH has been well advised in drawing up this collection of elegant solutions to the examples in his Conics." His treatise is just now in the full tide of success, and seems likely to maintain its position for some time yet before a better one drives it into the background. This, then, is just the time when such aid as is here furnished is most acceptable to teachers, "many of whom," as we have more than once stated in these columns, and as the author here testifies, "can ill afford time to write out detailed solutions of the questions which prove too difficult for their pupils." We have compared many of the solutions here given with our own (in manuscript), and find that new light is thrown on some by Mr. Smith's thorough command of the latest methods. We have detected here and there a trifling error, which may perhaps cause momentary trouble to a self-taught student, but there is sufficient detail given to enable the reader, on careful perusal, to make the required correction. In some cases more than one solution is given: this is a good feature. The possessor of the text-book and of the "Solutions" occupies a strong position, and should be able to attain considerable skill in this particular branch of mathematics. The Beginner's Guide to Photography. By a Fellow of the Chemical Society. (London: Perken, Son, and Rayment, 1888. THIS is a second edition, revised and enlarged, of an elementary guide for those commencing the art of photography. In it will be found practical hints as regards the choice of apparatus, and a good explanation of the whole process of photographic manipulation, written in a manner which for beginners leaves nothing to be desired. 66 An article on Exposure" has been added by Mr. H. S. Platts, including tables and directions, and the latter. if carried out by the amateur, ought to give him god results. There are, also, chapters on the production of lanternslides, enlarging, and photomicrography, and the book concludes with a collection of the illustrations referred to in it. LETTERS TO THE EDITOR. [The Editor does not hold himself responsible for opinionexpressed by his correspondents. Neither can he nnr. take to return, or to correspond with the writers rejected manuscripts intended for this or any other pul of NATURE. No notice is taken of anonymous communications.] Prophetic Germs. IN his letter of October 8, the Duke of Argyll says that he sees great value in my statement (which he improperly terms an "admission"), that natural selection cannot act upon any structure which is not already developed up to the stage of actua use. He says, "This is really all I want for my previous arg ment, because all organs whatever do actually pass through rud.mentary stages in which actual use is impossible." Here wt have the Duke's case in a nutshell. It is easily dealt with Firstly, what the Duke terms an "admission" on my part is as essential and explicitly stated element of Mr. Darwin's own exposition of his theory. Secondly, it is necessary for the Deko to demonstrate not that "all organs whatever," but that organs "do actually pass through rudimentary stages in which actual use is impossible. The stages here alluded to are-if I understand correctlyancestral stages, not stages in the embryological development the individual. I feel bound to state that I do not know of any facts in h history of either animals or plants which lead me (or, I may say, which have led any important number of the vast army of write » and observers on these subjects) to the conclusion that any exist ing active organ has passed through rudimentary stages in which actual use is impossible, if we set aside such cases as may b explained by correlation of growth or by the persistence : vestiges of formerly useful structures. If the Duke of Argyll can show that any one organ has (* "must have" passed through such useless stages (not explica le as due to correlation of growth nor as inherited vestiges, ought at once to do so. Mr. Darwin, in his severe testing of own theory, tried to find such cases, and did not find them. Wha are they? My own opinion is that they do not exist, and that the Duke's case collapses. E. RAY LANKESTER. A New Australian Mammal. A FEW days ago, through the kindness of Mr. A. Molineux. of Adelaide, a small mole-like animal, which appears to be new to science, was forwarded to the South Australian Museura. It was found on the Idracowie cattle-station, at a distance, I understand, of about 100 miles from the Charlotte Waters Telegraph Station, on the overland line from Adelaide to Port Darwin; but the exact circumstances of its capture are not ye to hand. The collector, however, reports that it must be ci rare occurrence, as, on questioning the aboriginals of the locality. there was only one old woman who said she had seen it before, and that upon a single occasion. It is evidently an underground burrowing animal resembling somewhat the Cape mole (Chrysochloris) in its general external appearance, but differing in many respects. The total length is 13 cm., inclusive of the tail, which is 2 era. long. The head, relatively shorter than Chrysochloris, has a rounded muzzle, the dorsal surface of which is covered by a horny shield. Nostrils transversely slit-like. No eyes visible, the skin passing uninterruptedly over the ocular region; but on reflecting the skin on one side of the face a small circular pigment spot is visible in the position of the eye. No apparen bony orbit. Tongue fleshy, broad at the base, and tapering to a blunt point. No external ears; but the ear-openings distinct. I mm. wide, and covered over with fur. The fore-limbs are short, resembling somewhat those of : mole; but the manus is folded, so that the large nails of the fourth and fifth digits only are visible in the natural position |