apex by means of a delicate transparent membrane. The single spiculum situated at the extreme end of the tail, projects slightly forwards, being surrounded by three skittle-shaped bodies. The tail of the female is curved upon itself, rounded off, and drawn out at the extreme end into a straight, beak-shaped point, whilst to both sides of the stumpy caudal extremity of the body, short vesicular elevations are attached. The female generative opening occurs at the commencement of the second half of the body.

"Judging by its external characters this genus is most closely allied to Strongylus."

The above description is supplemented by a more lengthened account of the internal organisation of the worm; this part of the record displaying in an especial manner those powers of accurate observation which so fully characterised the great systematist in helminthology prior to the time when he was deprived of his eye-sight.

Having communicated to Prof. Fletcher my views respecting the true history and identification of Stephanurus, he was pleased to supply me with some further particulars. Thus, (after receiving my reply) in his second communication (dated from Indianapolis, February 22), he says: "I at once renewed my researches, and was rewarded by finding the little saw-like teeth, upon a six-sided jaw, and, if I mistake not, two larger teeth or hooks. I also removed the lungs, heart, and liver, entire, from several hogs (just killed by shooting in the head) and found the worm, as before stated, in the liver, in all the hepatic vessels, and also in the vena cava. In some cases I found the eggs in abundance in the pelvis of the kidney, and in the urine, even when I could discover no cysts or worms about them."

Dr. Fletcher then alludes to the circumstance that he had since his first letter to me placed himself in correspondence with Prof. Verrill, who, it appears, had previously examined the worm. Prof. Fletcher also obligingly enclosed Prof. Verrill's paper, extracted from the American Journal of Science and Aris of September 1870, and, (in so far as I may be guided by its contents, it would now appear that the very first specimens which were obtained in the United States were the "five" examples sent by Dr. M. C. White, of New Haven, U.S., to Prof. Verrill, who adds :-" In the second instance, at Middleton, Conn., Dr. N. Cressy found large numbers of the worms in the fat about the kidneys of a young Suffolk pig, brought from New Jersey."

The title of Prof. Verrill's paper is, "Description of Sclerostoma pinguicola, a new species of entozoa from the hog."

made investigations in some Texas cattle (being cut up in our market) which damaged their sale a few years ago." In a third letter Dr. Fletcher tells me that greater facilities for examining the carcases of hogs had since been accorded him through the liberality of a Liverpool firm of pork packers, who had already killed 75,000 hogs during the summer season, i.e., up to the date of the first week in July. In hot weather the slaughtering is conducted in icehouses.

These practical observations by Dr. Fletcher appear to me to be of the highest importance, even though it should eventually turn out that there is no immediate connection between the occurrence of Stephanurus and the hog cholera epidemics. That this opinion rests upon substantial data seems probable from the circumstance that we have now not only received evidence of the occurrence of Stephanurus in Australia, but we are further apprised that the pigs which harbour it die of the disease superinduced by their presence. As I have already stated, in my second letter, published in the pages of the British Medical Journal, our earliest intelligence on this point rests upon the evidence furnished by a series of unnamed slides transmitted from Sydney to the President of the Royal Microscopical Society of London. Through the kindness of the Society's able Secretary, Mr. Slack, F.G.S., I was permitted to examine, identify, and name all the specimens, and it was then that I recognised Stephanurus amongst the number.

On the 4th inst. Dr. Morris's paper, which accompanied the specimens, was read to the Society. In that paper the author, like Prof. Verrill, expresses his belief that he has found a new entozoon, "its habitat being the fat surrounding the kidney of the pig." He speaks of it as occurring both in the "free and encysted state, the encysted being its final stage of existence," and, he adds, "its solid parts ultimately disappear, leaving a greyish brown fluid containing thousands of eggs." Those who desire further particulars in reference to the parasitism of pigs and sheep in Australia should consult Dr. Morris's paper, which will appear in the forthcoming November number of the Monthly Microscopical Journal. Dr. Morris speaks of the pigs as dying from some mysterious disease, and thinks "it is possible that this worm or its broed may be the cause." In some cases their death takes place quite suddenly, and this he supposes to be due to peritonitis set up by the swarming and migrations of the progeny. Be this as it may, it is interesting to notice the remarkable corsespondency of the conclusions arrived at by Dr. Fletcher and Dr. Morris independently. It will probably not be difficult to ascertain hereafter whether or not the maladies respectively termed "Hog Cholera" and "Mysterious Disease" are one and the same disorder; but whatever happens in this respect, it is now quite clear that this parasite, hitherto little regarded, and for many years past persistently overlooked, is extraordinarily prevalent in the United States, and, perhaps, equally so in Australia, it being further evident that its presence in the flesh of swine is capable of producing both disease and death. The statement of the worthy American farmer that the swallowing of infested flesh by a pig does not necessarily involve the pig-eating hog in a bad attack of a so-called "Cholera disease" requires to be further tested, and it also remains to be proven whether or not the Stephanurus be capable of passing through all its developmental changes from the egg to the adult form within the body of the bearer without having at some time or other gained access to the outer world. The comparatively large size of the ova, which I find to be about

is not without significance; but as yet we are unacquainted with the larval stages of growth. If no intermediary bearers are necessary to its development, we ought not to have to wait long for a complete record of the life-history T. S. COBBOLD of Stephanurus dentatus.

THE

BALL ON MECHANICS*

HE object of this book is to "prove the elementary laws of mechanics by means of experiments"-a method the exact opposite of that generally adopted. According to the usual method, a few very general principles are assumed as derived from experimental data, a group of intermediate principles is then obtained deductively, by the aid of which the action of forces in particular cases can be analysed. The particular cases may be such as have an interest from their bearing on practical questions, but they are only examples of a general method applicable to innumerable other cases. There are therefore two distinct objects for which mechanical experiments may be made-viz, either to verify the fundamental principles, or to verify the deductions drawn in particular cases. Experiments of the former kind are absolutely essential to the existence of the science. Unless, for instance, the conditions of the action of the force of friction are determined by experiment, no deductions as to cases into which that force enters have any but a theoretical value. The same is true in all similar cases; such questions as, whether quantity of matter is proportional to weight, whether gravity at a given station is sensibly a constant force, whether the elasticity of solid bodies follows Hooke's law, and if so within what limits, can be answered by experiment only. Such questions, on the other hand, as the tension of a tie-rod under given circumstances, the relation between the weights which keep a given lever at rest,

We will now give Mr. Ball's experiment in illustration of the same question :-"A piece of pine BE, 3'6" long and 1" x 1" in section (Fig. 2) is capable of turning roundits support at the bottom B by means of a joint or hinge; it is held up by a tie AC 3' long, which is attached to the support exactly above the joint. AB is r' long. From the point C a wire descends, having a hook at the end, on which a weight can be hung. The tie is attached to the spring balance, the index of which shows the strain The spring balance is supported by a wire strainer, by turning the nut of which the length of the wire can be shortened or lengthened as occasion requires. This is necessary, because when different weights are suspended from the hook the spring is stretched more or less, and the screw is then employed to keep the entire length of the tie at 3'. The remainder of the tie consists of copper wire" (p. 29). Mr. Ball then goes on to notice that when a weight of 20lbs. is placed on the hook, the strain, as determined by the spring balance, is 60lbs., thus verifying the analysis of the case given above.

As an example of an experiment of the former class we will take the following,-it is the form in which Mr. Ball

FIG. 1.

the relation between the power and the weight in a block and tackle, the form of the surface of a revolving liquid, admit of exact answers by deduction from the proper data, and, of course, the answers may be tested by experiment. Such experiments clearly have a different object from those of the former class. They have, indeed, this in common, that experiments of the latter kind also serve to verify fundamental principles, but they do so indirectly. It is, however, from the teacher's point of view that their value will be found greatest. In teaching the elementary parts of mechanics perhaps the greatest difficulty experienced is to make the learner feel that the diagrams drawn on the black board represent facts, that, for instance, the conclusion deduced from a triangle is really applicable to a crane. Put the experiment side by side with the deduction, and it will be seen that the experiment cannot fail to bring home to the mind of the learner that his reasoning relates to things and not merely to abstractions.

Let CB (Fig. 1) represent the jib or strut, and AB the tierod of a crane, the line AC being vertical. Let a weight P hang from A, and let it be required to determine the forces transmitted through the tie and the jib. P can be resolved into two forces acting along BC and AB produced, and an inspection of the figure will show that these forces bear to P the same ratio that the lines BC and AB bear to AC, and that the force along BC is a thrust, and that along AB a tension. This analysis is perfectly general.

* Experimental Mechanics: a Course of Lectures delivered at the Royal

College of Science for Ireland. By Robert Stawell Ball, M.A. With Illustrations. (London and New York: Macmillan and Co., 1871.)

FIG. 2.

gives Galileo's experiment of dropping bodies from the top of the Tower of Pisa. The figure (Fig.3) is so perfect that it scarcely requires explanation. So long as the current is in action, the horse-shoe G is magnetic, and a ball of iron F remains suspended from it. When the current is broken G is no longer magnetic and F falls. In this manner, by including the wire round both horse-shoes in the circuit, a ball of iron and one of wood, into which a flat-headed nail has been driven, can be kept suspended, and then by breaking the circuit they can be let fall at exactly the same instant, they are seen to reach the cushion at the same instant, and are thus shown to fall through equal spaces in the same time. Mr. Ball describes and discusses the experiment at some length, and shows how it proves that at a given station the attraction of gravitation on different bodies is proportional to their masses.

The above examples will give a better notion both of the contents and illustrations of the book than any long description. We may say, however, that the book con tains a clear and correct exposition of the first principles of mechanics, and illustrates, by well-chosen experiments, elementary. The figures reproduce all the circumstances all the points in the subject that can be fairly called of the experiments with so much exactness that with

amount of dispersion. It would be a very great mistake to suppose that the result is better with a very wide dispersion. This, of course, makes the spectrum larger, but very greatly impairs the definition of the absorption-bands. Everyone who has had experience with an ordinary microscope must be well aware that a particular magnifying power is best for each particular class of object or kind of structure, and that in some cases nearly all the important characters would be lost by employing too high a power; but at the same time too low a power would be equally disadvantageous in other respects. This analogy holds good in the case of the dispersion of prisms. The power ought to be regulated by the character of the absorption bands. If they are dark, narrow, well-defined, and lie close together, as in the case of partially opaque crystalline blow-pipe beads of borax containing deposited crystals of oxide of lanthanum with oxide of didymium, a somewhat powerful dispersion is not only admissible, but quite necessary to separate some of the bands. If, however, they are broad and faint like those seen in the spectra of many of the colouring matters found in animals and plants, a powerful dispersion spreads them over such a wide space, and makes the shading off so gradual, that the eye can scarcely appreciate the extra amount of absorption; whereas, when a lower dispersive power is used, a well-marked absorption-band can easily be seen. This is more especially the case with impure mixtures. I have found that when it was requisite to examine a mixed, somewhat turbid, coloured solution to detect, if possible, the presence of some substance which, when alone, gave a spectrum with distinct absorption-bands, no trace could be recognised by means of a prism of high dispersive power; but it could be detected without any difficulty with a lower. In carrying on practical investigations it is far more important to be able to succeed in such a case than to exhibit on a large and more imposing scale the spectra of a few substances which give dark and welldefined bands. There can be no doubt that it is a great advantage to have a number of prisms of different dispersive power, so that in all cases the most suitable may be used; but at the same time some observers might not wish to have more than one, and thus it becomes important to decide what amount of dispersion is the best for the generality of objects-is sufficiently great to divide narrow, closely-placed bands, and yet not so great as to prevent our seeing broad and fair ter. No magnifying power whatever is applied to the spectrum itself in the instrument now under consideration.

As described in some of my former papers,* the compound, direct-vision prisms first made for me by Mr. Browning were composed of two rectangular prisms of not very dense flint glass, and three of crown glass, one being rectangular, and the others of an angle of about 75°. This combination gives a dispersive power, which shows faint bands very well; but is not enough to divide the narrow and close bands seen in the spectra of a few substances. Mr. Browning then made prisms of similar construction, only that very dense flint glass was employed; This combination gives about double the former dispersion, which divides narrow and close bands admirably, but sometimes shows broad and fainter bands so very badly that they can scarcely be recognised. It thus appeared to me that, if only one compound prism be supplied with the instrument, the best dispersive power would be intermediate between these two extremes. At the same time much would depend on the particular purpose to which the instrument was applied, and also, to some extent, on the individual differences between different observers. Mr. Browning has described † the plan that he probands by means of a bright line, seen by reflection from for the measurement of the position of absorptionposes the surface of the prism, moved backwards and forwards * Popular Science Review, vol. v., 1866, pp. 66-77; Brit. As. Report, 1865 (pt. 2), p. 11.

Monthly Microscopical Journal, vol. iii. p. 68.

North America. He examined all the principal collections of shells in the United States and Canada, and especially those made in the deep-sea explorations of the Gulf of Florida and Gulf of St. Lawrence. The former was in the charge of Dr. Stimpson at Chicago; and Mr. Jeffreys was entrusted with specimens (some of them unique) of all the species which appeared to him the same as certain undescribed species dredged by him in the depths of the East Atlantic during the Porcupine expeditions of 1869 and 1870. These specimens may be the only ones saved from the Museum of the Academy of Sciences at Chicago, which it is greatly feared was destroyed by the late deplorable conflagration. Several species of North American land and freshwater shells will also be found to inhabit the eastern hemisphere, although bearing different names. Through the kindness of Prof. Baird, Mr. Jeffreys had an opportunity of dredging on the coast of New England in a Government steamer; and he everywhere received great hospitality and attention. He particularly acknow. ledges his obligation to Mr. Anthony, Prof. Agassiz, and Prof. Shaler, of Cambridge; the Hon. S. Powel, of Newport, R. I.; Prof. Baird, of Washington; Prof. J. C. Draper, of New York; Mr. Binney, of Burlington, N.J.; Dr. Isaac Lea, of Philadelphia; Dr. Stimpson and Mr. Blatchford, of Chicago; and to Principal Dawson and Sir W. E. Logan, of Montreal.

Les Mondes records the death of M. Henri Lecocq, Professor in the Faculty of Sciences at Clermont Ferrand, eminent both as a botanist and geologist. His life has been spent in encouraging and assisting the cultivation of the sciences to which he especially devoted himself; and by his will he has devoted his property to the same end. He leaves to the town where he resided the sum of 150,000 francs, of which 50,000 is bestowed on the botanic garden established by him, 50,000 to the maintenance of water-supply and fountains, and 50,000 to the establishment of covered markets. M. Lecocq leaves besides to the town all his collections of natural history, zoology, botany, geology, and mineralogy, as well as all the cabinets which contained them.

MR. ALFRED HENRY GARROD, scholar in natural science of St. John's College, Cambridge, and formerly Demonstrator in Physiology to Prof. Humphry, has been appointed Prosector to the Zoological Society of London. There is probably no other post in the world which affords opportunities for the study and advancement of animal physiology and comparative anatomy equal to those enjoyed by the possessor of this office, owing to the extraordinary extent of the Society's vivarium in the Regent's Park. Mr. Garrod, we understand, will not enter upon his duties until the beginning of the new year.

MR. DAVIDSON, of King William's College, Isle of Man, has been elected a Scholar in Natural Science at Sidney Sussex College, Cambridge.

A SCHOLARSHIP is announced at Balliol College, Oxford, on the foundation of Miss H. Brakenbury, "for the encouragement of natural science," of the value of 70/. for three years. This is open to all candidates who have not exceeded eight terms from matriculation. The examination begins on Tuesday, November 21. Papers will be sent in (1) Mechanics and Physics, (2) Chemistry, (3) Physiology, but no candidate will be expected to take up more than two subjects at the most. There will also be a practical examination in the above subjects. Further information can be obtained from the tutors.

We understand that the next number of the Contemporary Review will contain an important article by Prof. Huxley in comment on some portions of Mr. Mivart's "Genesis of Species." THE following are among the Publishers' announcements of scientific works for the approaching season:-From Messrs. Longmans:-The Royal Institution, its Founder and its First Professors

by Dr. Bence Jones, Hon. Sec. ; Spectrum Analysis in its Application to Terrestrial Substances and Physical Constitution of the Heavenly Bodies, familiarly explained by Dr. H. Schellen, with Notes by William Huggins, LL.D., D.C.L, F.R.S, I vol. 8vo. with coloured plates and other illustrations; a Smaller Star Atlas, for the use of schools and junior students of Astronomy, by R. A. Proctor, B. A., F.R.A.S., in twelve circular coloured maps and two index maps, with an introduction showing how the stars may be recognised and their motions studied and understood; Popular Lectures on Scientific Subjects, by Prof. Helmholtz, translated by H. Debus; Elements of Materia Medica and Therapeutics, being an abridgement of the late Dr. Pereira's Materia Medica, and comprising all the medicines of the British Pharmacopoeia, together with such others as are frequently ordered in prescrip. tions, and required for the use of medical practitioners, edited by Robert Bentley. From Mr. Murray :-The Principles of Geology, or the Modern Changes of the Earth and its Inhabitants considered as illustrative of Geology, by Sir Charles Lyell, Bart., F.R.S., 11th edition, thoroughly revised, illustrations, Vol. 1 ; The Metallurgy of Copper, Zinc, and Brass, including Descriptions of Fuel, Wood, Peat, Coal, Charcoal, Coke, Fire-Clays, by John Percy, F.R.S., new edition, revised, many illustrations. From Messrs. Macmillans :-A Treatise on the Origin, Nature, and Varieties of Wine, being a complete manual of Viticulture and Enology, by J. L. W. Thudichum, M.D., and August Dupré, with numerous illustrations; the Ministry of Nature, by the Rev. Hugh Macmillan; a series of Science Primers, under the joint editorship of Profs. Huxley, Roscoe, and Balfour Stewart; the following will be ready about Christmas: Introduction, by Prof. Huxley; Chemistry, by Prof. Roscoe; Physical Science, by Prof. Balfour Stewart. From Messrs. Bell and Daldy :-Alpine Plants, containing more than one hundred coloured illustrations of the most striking and beautiful Alpine flowers, with descinetions by D. Wooster. From Messrs. Deighton, Bell, and Co :The Desert of the Exodus, Journeys on Foot in the Wilderness of the Forty Years' Wanderings, by E. H. Palmer, M. A., Fellow of St. John's College, with maps and illustrations from photo. graphs and drawings taken on the spot by the Sinai Survey Expedition, and C. F. Tyrwhitt Drake. From Mr. Good win :-A new and greatly-improved edition of What are the Stars? a treatise on Astronomy, by Mary Storey Lyle. From Messrs. Rivingtons :-Elementary Statics, by Hamblin Smith, 3rd edition, revised and corrected; Geometrical Conic Sections, by G. Richardson, M.A., Assistant-Master at Winchester College, and late Fellow of St. John's College, Cambridge; Analytical Geometry of Two Dimensions, by H. E. Oakley, M. A., late Fellow and Senior Mathematical Lecturer of Jesus College, Cambridge, H. M. Inspector of Schools. From Messrs. Cassells :Elementary Astronomy, by Richard A.Proctor, B. A., F. R. A. S., with nearly fifty original illustrations; Elementary Geography, by Prof. D. T. Ansted, M.A., F. R.S., Examiner in Physical Geography in the Department of Science and Art, illustrated with original diagrams.

WE are glad to learn that the Rev. E. Smith and Mr. Irving are busy with a new and complete flora of the neighbourhood of Nottingham, which we hope will ultimately include the whole of that county. The work is being done under the auspices of the Literary and Philosophical Society of Nottingham.

DR. PETERMANN has written to several German papers to announce the success of a new German Arctic Expedition. According to a telegram received by him a few days ago, and since confirmed, Lieutenants Weyprecht and Payer have penetrated to 79° N. latitude, and have actually discovered the open Arctic Sea, which has been so long searched for. They employed a Norwegian sloop, and penetrated northwards between Spitzbergen and Nova Zembla, and they report an open sea from 42° to 60° E. lorgitude, and that but little ice was