equation, with the result of wholly falsifying all that follows. On the other hand, we must fully recognize that, when more formidable analysis is really required (as, for instance, in the treatment of v. Helmholtz's monocyclic and polycyclic systems), M. Poincaré seems to feel so thoroughly at home as to criticize with freedom.

One test of the soundness of an author, writing on Thermodynamics, is his treatment of temperature, and his introduction of absolute temperature. M. Poincaré gets over this part of his work very expeditiously. In §§ 15-17 temperature, t, is conventionally defined as in the Centigrade thermometer by means of the volume of a given quantity of mercury; or by any continuous function of that volume which increases along with it. Next (§ 22) absolute temperature, T, is defined, provisionally and with a caution, as 273 +1; from the (so-called) laws of Mariotte and Gay-Lussac. Then, finally (§ 118), absolute temperature is virtually defined afresh as the reciprocal of Carnot's function. [We say virtually, as we use the term in the sense defined by Thomson. M. Poincaré's Fonction de Carnot is a different thing.] But there seems to be no hint given as to the results of experiments made expressly to compare these two definitions. Nothing, for instance, in this connection at all events, is said about the long-continued early experimental work of Joule and Thomson, which justified them in basing the measurement of absolute temperature on Carnot's function.

In saying this, however, we must most explicitly disclaim any intention of charging M. Poincaré with even a trace of that sometimes merely invidious, sometimes purely Chauvinistic, spirit which has done so much to embitter discussions of the history of the subject. On

the contrary, we consider that he gives far too little prominence to the really extraordinary merits of his own countryman Sadi Carnot. He writes not as a partisan

but rather as one to whom the history of the subject is a matter of all but complete indifference. So far, in fact, does he carry this that the name of Mayer, which frequently occurs, seems to be spelled incorrectly on by far the greater number of these occasions! He makes, however, one very striking historical statement (§ 95):

“Clausius . . . lui donna le nom de Principe de Carnot, "bien qu'il l'eût énoncé sans avoir connaissance des "travaux de Sadi Carnot."

Still, one naturally expects to find, in a Treatise such as this, some little allusion at least to Thermodynamic Motivity; to its waste, the Dissipation of Energy; and to the rest of those important early results of Sir W. Thomson, which have had such immense influence on the development of the subject. We look in vain for any mention of Rankine or of his Thermodynamic Function; though we have enough, and to spare, of it under its later alias of Entropy. The word dissipation does indeed occur, for we are told in the Introduction that the Principe de Carnot is "la dissipation de l'entropie."

We find Bunsen and Mousson cited, with regard to the effect of pressure upon melting points, almost before a word is said of James Thomson; and, when that word does come, it wholly fails to exhibit the real nature or value of the great advance he made.

Andrews again, à propos of the critical point, and his splendid work on the isothermals of carbonic acid, comes

in for the barest mention only after a long discussion of those very curves, and of the equations suggested for them by Van der Waals, Clausius, and Sarrau:-though his work was the acknowledged origin of their attempts.

The reason for all this is, as before hinted, that M. Poincaré has, in this work, chosen to play almost exclusively the part of the pure technical analyst; instead of that of the profound thinker, though he is perfectly competent to do that also when he pleases. And, in his assumed capacity, he quite naturally looks with indifference, if not with absolute contempt, on the work of the lowly experimenter. Yet, in strange contradiction to this, and still more in contradiction to his ascription of the Conservation of Energy to Mayer, he says of that principle:"personne n'ignore que c'est un fait expérimental."

Even the elaborate thermo-electric experiments of Sir W. Thomson, Magnus, &c., are altogether ignored. What else can we gather from passages like the following?

(§ 287) "Sir W. Thomson admet qu'il existe une "force electromotrice au contact de deux portions d'un "même conducteur à des températures différentes; il "assimile donc ces deux portions à deux conducteurs "de nature différente, assimilation qui parait très vrai"semblable."

(§ 291) ".. si l'effet Thomson a pu être mis en "évidence par l'expérience, on n'a pu jusqu'ici constater "l'existence des forces electromotrices qui lui donnent "naissance."

Everyone who comes to this work of M. Poincaré fresh from the study of Clerk-Maxwell's little treatise (or of the early papers of Thomson, to which it owed much) will feel as if transferred to a totally new world. Let him look, for instance, at Maxwell's treatment of the Thermodynamic Relations, Intrinsic and Available Energy, &c., and then turn to pp. 148-150 of M. Poincaré's work. There he will find at least a large portion of these most

important matters embodied in what it seems we are now to call the Fonctions caractéristiques de M. Massieu !

But the most unsatisfactory part of the whole work is, it seems to us, the entire ignoration of the true (ie. the statistical) basis of the second Law of Thermodynamics. According to Clerk-Maxwell (NATURE, xvii. 278)

"The touch-stone of a treatise on Thermodynamics is "what is called the second law."

We need not quote the very clear statement which follows this, as it is probably accessible to all our readers. It certainly has not much resemblance to what will be found on the point in M. Poincaré's work:-so little, indeed, that if we were to judge by these two writings alone it would appear that, with the exception of the portion treated in the recent investigations of v. Helmholtz, the science had been retrograding, certainly not advancing, for the last twenty years. P. G. T.

towards the suppression of the insect pests of cultivated plants. One effect of this welcome energy has been a process of differentiation, whereby the attacks of insects upon crops, instead of being included in the comprehensive but somewhat incomprehensible term of "blight," have been separated one from another, more or less clearly defined, and, to a very useful extent, associated respectively with the ravages of certain specific insects. It is now possible for those to whom the subject is new to obtain a much clearer idea of the scope of agricultural entomology than was the case even as recently as five or six years ago. "The time has arrived," observes the author, "when, if we are to fight insect pests successfully, united action must be taken, and knowledge gained by constant vigilance, and by useful and carefully conducted experiments. Only thus can a better knowledge be obtained of the relations of insects to agriculture, viticulture, and horticulture."

About one-fifth of this volume of 150 pages is devoted to an introduction to entomology, a classification of insects, directions for collecting and preserving specimens of economic interest, the preservation of insect-destroying birds, and certain horticultural quarantine rules. The main part of the book is occupied with a discussion of fourteen of the most troublesome insect pests of apples, pears, apricots, and cherries in the colony of Victoria. These are illustrated by means of coloured plates, the excellence of which demands a word of approbation. The evergrowing facilities for international transport are, no doubt, partly responsible for the extent to which the insect pests of this country are identical with those of the Antipodes. In this connection it is worthy of note that at least five of the pests which are illustrated have acquired as unenviable a reputation in Britain as in Victoria. These are the woolly Aphis (or American blight), the codlin moth, the apple-bark scale, the red spider (an Arachnid), and the pear and cherry slug, which is the slimy, repulsive-looking, leaf-eating larva of one of the saw-flies. Of the fourteen pests enumerated, the Lepidoptera claim four, Coleoptera three, Homoptera two, Heteroptera two, Arachnoidea two, and Hymenoptera one.

The volume concludes with an instructive chapter upon insecticides and the means for applying them. Amongst the more noteworthy of the former are carbon bisulphide, Gishurst compound, hellebore powder, kerosene petroleum), gas lime, London purple, Paris green, sulphur, and tobacco. A caution is given as to the use of certain so-called insecticides, such as ammonia and carbolic acid. Insecticides they undoubtedly are, but inasmuch as they injure the plant as well as kill its pests, they had better be left alone. Various kinds of apparatus for applying insecticides are described, and illustrated by means of twenty wood-cuts. The most efficient and one of the newest of these, the air-power distributor called the Strawsonizer-after its inventor, Mr. G. F. Strawson, an Englishman,-is adequately described and figured. Several useful nozzles and pumps are likewise noticed.

Mr. French has produced a volume of much practical value, and it may be hoped that he will maintain the same high standard in the subsequent parts. One appeal, however, may be made to the author-and not only to him but to all writers upon this subject,—and that is to append the name of the authority to the systematic name of each

Whether agriculture is a subject that can be at all satisfactorily treated, in a book of the type which a "reader" necessarily suggests, is a question that need not be discussed here. But it is abundantly evident that the problem has not been solved in the volume under notice. It is sprinkled with footnotes and tables, the latter being of as complicated a character as any which are usually found in agricultural treatises. Then, again, there are long quantitative lists of grass seeds recommended for use in laying land down to pasture, and these, it is to be feared, will be found both wearisome and unintelligible to the small boy who has to wade through them in the course of a "reading lesson." Indeed, the book is curiously unequal throughout, and it is apparent that the author would probably have done better had he not had to continually remind himself that he was writing a "reader" for children.

It is particularly desirable that, in a strictly elementary book, everything should be correct; but this is hardly the case with some of the illustrations. In Fig. 2, for example, the fruit of the cabbage is represented as dehiscing from above downwards, though this is not the behaviour of a siliqua in nature. On the other hand, the figures of grasses are exceedingly good.

The text is not free from errors. On p. 67 is described what will happen "if turnips braid (sic) too thickly." The use of systematic names will rather hinder the juvenile student than otherwise, unless special care is taken to render them correctly, which is not always the case. Occasionally, the fanciful element is in evidence, as when it is stated (p. 207): "Mowing is as old as Time itself; for has not Time been represented as carrying a scythe over his shoulder?"

"In future editions," it is said in the preface, "this little book may, no doubt, be further extended." It is questionable, however, whether the author would not of the kind which appears to be contemplated, by eliminmore successfully meet the requirements of a "reader," ating all such matters as do not fall easily into the course of a reading lesson. At present, it would seem as if the object had been to produce a text-book" rather than a "reader."

66

Arithmetic for Schools. By Charles Smith. "Pitt Press Mathematical Series." (Cambridge: University Press, 1891.)

MR. CHARLES SMITH is such a well-known writer of mathematical works that we expected to find the present volume very commendable. In this we are not disappointed. The explanations of the fundamental principles

66

and processes are treated with a clearness, conciseness, and completeness that make the book a delight to read, and although, as he says, my aim has not been to introduce novelties," yet he has succeeded, in so far as we are able to predict, in placing before students a book not only of practical utility, but also of great educational value. Stocks and shares, and such like transactions, have all been treated more in accordance with the methods of the present day than is usual in such treatises. There has also been inserted a chapter on foreign exchanges for the benefit of those preparing for examinations in commercial arithmetic. The examples are of a varied and useful nature, and are numerous and well chosen : each new principle or process is accompanied with one or two sets of them, while interpolated throughout are many to be worked out by those who wish to revise their back work as they proceed in the subject. Miscellaneous exercises to the number of 500, together with sets of examination papers, form also a useful addendum. W.

Journeys in Persia and Kurdistan. By Mrs. Bishop (Isabella L Bird). Two Vols. With Portrait, Map, and Illustrations. (London: John Murray, 1891.) THIS work consists of letters written in the course of the second half of journeys in the East which extended over a period of two years. The author had intended, in the event of their being published, to correct them by reference to notes made with much care. Of these notes she was robbed, and she refers to the loss as her "apology to the reader for errors which, without this misfortune, would not have occurred." Perhaps, however, the book is all the better for being presented essentially in the form in which it was originally written. The record of the writer's impressions has thus a directness, simplicity, and freshness of which it might to some extent have been deprived by elaborate revision. Mrs. Bishop does not profess to have written a book on Persia and Eastern Asia Minor. She has merely set down what she herself saw during her travels in those countries. But she has done this so well that ordinary readers are not likely to resent the slightness of her references to the administration of government, the religious and legal systems, the tenure of land, and the mode of taxation. The illustrations are very good, and add considerably to the interest of the narrative.

A First Book of Electricity and Magnetism. By W. Perren Maycock, M. Inst. E.E. (London: Whittaker and Co., 1891.)

THE Scope of this work is limited to the syllabus of the elementary stage of the Science and Art Department. It is intended as an easy introduction to many of the text-books now in use, which, although termed elementary, are of rather too advanced a nature for some students to commence with; the author considering that they might be led to "take a greater interest in their work" by the help of such a book as he has put before us. Throughout the three parts, which deal severally with magnetism, electro-kinetics, and electro-statics, the explanations are of a plain and simple nature, while the illustrations bring out clearly the various points which they are intended to exhibit. The information is based on the latest ideas; and interpolated in the text are many questions, the answers to which the student should write out before proceeding beyond them.

The book will be found really very useful for beginners, and will be to them a good introduction to higher works. A Cyclopædia of Nature Teachings. With an Introduction, by Hugh Macmillan, LL.D., F.R.S.E. (London: Elliot Stock, 1892.)

THE Compiler of this volume has brought together a large number of extracts from various authors, setting forth

what profess to be "facts, observations, suggestions, illustrations, examples, and illustrative hints taken from all departments of inanimate nature." Here is the information offered to us about "the sun-controlled stars" :

"When stars, first created, start forth upon their vast circuits, not knowing their way, if they were conscious and sentient, they might feel hopeless of maintaining their revolutions and orbits, and might despair in the face of coming ages. But, without hands or arms, the sun holds them. Without cords or bands, the solar king drives them unharnessed on their mighty rounds without a single misstep, and will bring them in the end to their bound, without a single wanderer."

This sorry stuff is a fair specimen of a good many of the "Nature Teachings" presented in the "Cyclopædia." A more suitable title for the compilation would have been "Scientific Gush." The compiler does not always even give accurate titles to his extracts. A passage from one of Mr. Ruskin's writings has the strange heading, “The Star Mercury."

LETTERS TO THE EDITOR.

[The Editor does not hold himself responsible for opinions expressed by his correspondents. Neither can he undertake to return, or to correspond with the writers of, rejected manuscripts intended for this or any other part of NATURE. No notice is taken of anonymous communications.]

On the Attitudes of the Zebra during Sleep, and their Influence on the Protective Value of its Stripes. NOWADAYS, when the colours of animals and their uses for the purposes of recognition and protection are forcing themselves upon the attention of all naturalists, it is not wonderful that an animal so conspicuously marked as the zebra should have commanded a large share of notice.

Much as it has been considered, however, I do not think we have yet learned all the lessons that it has to teach us.

That its bold and vivid stripes should be of immense service for recognition may be accepted as beyond dispute.

The statement of Mr. Francis Galton, that on a clear moonlit night these vivid stripes melt into invisibility, and to an eye not absolutely focussed to the animal itself, but to objects in its immediate vicinity, it is quite unseen, even when so near that its breathing can be heard distinctly, proves most indubitably their immense protective value. As he says, "If the black stripes were more numerous, it would be seen as a black mass; if white, then as a white one; but their protection is such as exactly to match the pale tint which arid ground possesses in the moonlight."

Prima facie, this is hardly what one would have expected, but when pointed out by a competent and trustworthy observer, even a slight knowledge of the laws of light proves it to be true.

Let anyone notice at what a short distance a lady in a galatea dress with broad stripes becomes invisible in the moonlight, and he will be at once convinced of the truth of Galton's

remark.

Prof. Henry Drummond further says:-"When we look at the coat of a zebra, with its thunder-and-lightning pattern of black and white stripes, we should think such a conspicuous object designed to court, rather than elude, attention. But the effect in nature is just the opposite. The black and white somehow take away the sense of a solid body altogether, and the two colours seem to blend into the most inconspicuous grey, and at close quarters the effect is as of bars of light seen through the branches of shrubs. I have found myself in a forest gazing at what I supposed to be a solitary zebra, its presence betrayed by some motion due to my approach, and suddenly realized that I was surrounded by an entire herd, which was all invisible until they moved." By this I understand Prof. Drummond to refer to his observations in the day-time, as Mr. Galton speaks only of the moonlight.

One can readily see how the shadows of the branches in a tropical forest falling upon the zebras would so intermingle with the stripes of the animals as to add enormously to the difficulty of recognition by human eyes, and also, in the dim light of the

forest (broken up as it is into bars of light and shade), by the eyes of their fierce and hungry foes as well.

A careful examination of the varied stripes of the zebra has forced upon my mind the conviction that they have a still deeper meaning and value than has hitherto been noticed and explained.

It is easy to see how the vertical bars may assimilate to the falling shadows in the noonday sun, and the diagonal stripes on the neck and hind-quarters to those cast by the declining day. But it is not so much in the day-time and during its waking hours that the zebra stands in such pressing need of concealment as at night, when it is compelled to rest. Then, when surrounded by eager and wakeful foes, it does require all the concealment it can get. Now, let us suppose the animal to be lying down, say partly on its side and partly on its belly, as horses very frequently do. What will be the effect of such an attitude upon the different stripes on various parts of the body? In the first place, the animal will thrust out its knees, and fold its fetlocks backwards under its body in such a manner that the horizontal bars on the fore-legs will become vertical.

At the same time it will push out in a backward direction, its haunches, and the hind-feet will be brought forward under or near its body, so that the diagonal stripes on the hind-quarters will be drawn so as to become much more vertical, and to correspond with the now vertical bars across the hind-legs, made vertical by the folded position of the limbs. In such an attitude-a perfectly natural and common one-all the stripes of the body will be vertical, or nearly so, especially if the zebra rests its head upon the ground, or its fore-legs, so as to bring the diagonal stripes of its neck into unison with all the rest. Supposing, then, that a coincidence in the general direction of the stripes is produced by such an attitude of the body during rest, is it too much to assume it to be an extension and refinement of those protective devices of Nature, extending to the sleeping zebra the full amount of all the possible protective value of its stripes just at the very time when it needs it most, so that in the clear tropical moonlight, when the shadows are only a little less distinct than in the day, it may be able to repose in something like safety and peace?

But, suppose the zebra rests, not always on its belly, as suggested, but now and then on its side, with its limbs outstretched. It is plain that the vertical, diagonal, and horizontal stripes would then be all more horizontal than anything else, but pointing in different directions, and would then so assimilate themselves with the crossed and varying directions of the shadows as to have the same practical effect in hiding the sleeping animal from its foes.

Under such a supposition (by no means an impossible one), it seems to me that those beautiful bars of brown and white surround the dormant zebra with a protection and a defence almost as secure as bars of iron or brass, leaving the foes with nothing but their sense of smell to guide them to their prey.

We have only to assume the folding up of the limbs, like the folding up of a two-foot rule, until the marks on both sides correspond, and we see at once the unification in the general direction of all the stripes of the body, which I cannot help believing has a very considerable protective value to the zebra.

However, if any enlightened and generous patron of science would kindly present to our College ("Owens," Manchester) a good stuffed specimen of a recumbent zebra in the attitude I have suggested, he would help considerably to settle a nice point in the matter of protective colouring, and give to the cause of scientific education a very welcome and appreciable aid. December 21, 1891.

H. W.

The Migration of the Lemming. THERE are two questions which I should like to ask Mr. W. Duppa-Crotch touching his recent letter on the above subject (NATURE, December 31, p. 199); and for this purpose I had better begin by quoting a paragraph from my own discussion of the same subject, written close upon ten years ago :

"Looking to Mr. Collett's large experience on the subject, as well as to the intrinsically probable nature of his views, I think we may most safely lend countenance to the latter. The most important point of difference between Mr. Crotch and Mr. Collett has reference to a question of fact. For while Mr. Crotch states that the migrations are made westwards without reference to the declivities of the country, Mr. Collett is emphatic in saying that 'the wanderings take place in the direc

tion of the valleys, and therefore can branch out from the plateaux in any direction.' If this is so, there is an end of Mr. Crotch's theory, and the only difficulty left to explain would be why, when the lemmings reach the sea, they still continue on their onward course to perish in their multitudes by drowning. The answer to this, however, is not far to seek. For their ordinary habits are such that when in their wanderings they come upon a stream or lake, they swim across it; and therefore when they come upon the coast line it is not surprising that they should behave in a similar manner, and, mistaking the sea for a large lake, swim persistently away from land with the view to reaching the opposite shore, till they succumb to fatigue and the waves. Therefore, pending further observations on the question of fact above alluded to, cannot feel that the migration of the lemming furnishes any difficulty to the theory of evolution over and above that which is furnished by the larger and more important case of migration in general, to the consideration of which I shall now proceed" ("Mental Evolution in Animals," pp. 284-85).

Mr. Duppa-Crotch's theory thus alluded to-which constituted the most striking feature of his "rather lengthy paper before the Linnean Society," and which, he then wrote, "led me to spend two years in the Canaries and adjacent islands"is, briefly, as follows:

:

It is

"I allude to the island or continent of Atlantis. evident that land did exist in the North Atlantic Ocean at no very distant date. . . . Is it not then conceivable, and even probable, that, when a great part of Europe was submerged, and dry land connected Norway and Greenland, the lemmings acquired the habit of migrating westwards, for the same reasons which govern more familiar migrations? It appears to

me quite as likely that the impetus of migration towards this continent should be retained, as that a dog should turn round before lying down on a rug, merely because his ancestors found it necessary thus to hollow out a couch in the long grass" (Linn. Soc. Journ., vol. xiii. p. 30).

And, in a subsequent paper (ibid., p. 157 et seq.), he combats the statement of Mr. Collett, "that these migrations follow the natural declivities of the country." Now, however, it appears that Mr. Collett turns out to be right as to the fundamental fact of the migrations not being westerly more than towards any other point of the compass; for Mr. DuppaCrotch, in his letter to you, acknowledges that, in regard to this point, which he previously maintained against Mr. Collett, he was betrayed into an error by trusting to common report and insufficient personal experience." Nevertheless, he still maintains that the lemmings in their migrations "do not follow the water-shed."

The questions, therefore, which I have to put are: (1) What are the grounds on which Mr. Duppa-Crotch continues to differ from Mr. Collett touching this minor point?; and (2) Does he still maintain his theory with regard to "the island or continent cf Atlantis," since he has found himself in error upon the major point? GEORGE J. ROMANES.

Christ Church, Oxford, January 6.

Destruction of Immature Sea Fish.

IT might be supposed that the "importance of the subject" would have induced Mr. Walker, at all events, to examine Dr. Fulton's observations at first hand, before criticizing them (NATURE, December 24, 1891, p. 176), instead of confining himself to reading a review.

It may be pointed out that Dr. Fulton's computation of the number of young fish captured is intended to apply only to the Solway, as indeed may be gathered from your review, and being, not a matter of hearsay, as implied by Mr. Walker, but founded on an average of fifteen hauls extending over nine months of the year, is likely to be pretty near the mark.

In examining Mr. Walker's own computation, we find that he reckons six days' fishing to the week, instead of four, which is Dr. Fulton's estimate, based on local inquiry; and we may say that, if Mr. Walker has succeeded in utilizing every working day during any one year of his trawling career, he must have been singularly fortunate in his weather, or must have confined himself to very sheltered waters. I think it will be conceded that a calculation derived from actually counting the catch is more trustworthy than one derived from an observation (or was it only an estimate?) of weight. If, however, "10 cwt. of young flukes, . . . not one the size of half-a-crown," is really only the

sixtieth part of a day's destruction in the Formby Channel, it is a wonder that there are any left.

A point emphasized in the review, but seemingly missed by Mr. Walker, is that the young fish are always promptly returned to the sea by the Solway shrimpers, and the fact that the industry flourishes in spite of the delay so caused shows that the destruction which ensues from the practices described by Mr. Walker is quite unnecessary. Dr. Fulton has experimentally proved that the proportion of young flat-fish of a certain size (say above an inch) that would not survive if returned to the sea is small, so that it is evident that Mr. Ascroft's "axiom that 90 per cent. of fish that come on board a boat is destroyed' holds good from no fault of the trawl itself, but simply from a discreditable carelessness on the part of the man.

Mr. Walker's experiences at the mouth of the Dee show that the shrimps and the young soles (species ?) have different habitats in that river, so that his suggestions as to the limitation of shrimp-trawling seem rather superfluous, since it may be supposed that the trawler would fish where he knew he could get shrimps, and not go out of his way to catch what he did not want. I have noticed myself on the west coast of Ireland that the minute post-larval flat-fish, smaller than those dealt with by Fulton, and which are undoubtedly killed by the meshes of the shrimp-trawl, were never taken on ground frequented by shrimps, where, indeed, as one may judge from

one can see immediately that for the latitude of London at that remote period, the Cross would be seen at the southern horizon, and that Sirius then did not rise at all. K. HAAS. Vienna.

Simple Proof of Euclid II. 9 and 10.

IN NATURE of December 24 (p. 189) a simple proof of Euclid II. 9 and 10 is given, which it is stated is believed to be new. It may therefore be of interest to your readers to know that these proofs are given in an edition of Euclid which we have now in the press. As the author, Mr. Brent, is resident at Dunedin, New Zealand, we are unable to state whether he lays claim or not to any originality in respect to them in any case, as he has been engaged in mathematical teaching for many years, these and similar proofs of other propositions in Euclid II. have clearly been more widely employed than has been supposed. PERCIVAL AND CO.

34 King Street, Covent Garden, London, January 4.

THE ALLEged discoVERY OF A BACILLUS IN INFLUENZA.

have a poor chance of surviving.

Everyone will agree with Mr. Walker that it is most necessary to ascertain the habitat of the young fish at different times of the year, and to this end the energies of the Marine Biological Association in England, the Fishery Board in Scotland, and the Royal Dublin Society in Ireland, have been for some time directed; and the assistance that might be rendered by a series of observations by one possessing the experience and opportunities of Mr. Walker would be incalculable. Until, however, our knowledge on the subject is much more complete, I question the advantage of strewing boulders about the bottom of the sea. Even if they remained to accomplish their purpose of interfering with trawling, there is the danger that they would form an attractive shelter, not to the young flat-fish that stand in no need of it, but to some of their natural enemies. Dublin, December 27, 1891. ERNEST W. L. HOLT.

The globe is fastened in a ring, so that it can be turned round an axis that goes through the poles of the ecliptic, but can also be fixed in any position by a pair of screws. The amount of turning is to be measured by a divided circle.

The ring above mentioned-which we will call ring I.-is movable in another ring (ring II.), round an axis, which forms a right angle with the axis formerly mentioned. The inclination between ring I. and ring II. can be measured by an index; it must equal the obliquity of the ecliptic.

Ring 11. is fastened finally in a third and extreme ring (ring III.), so that it can be turned round an axis which forms an angle of 90° with the axis of ring II. Ring III. is mounted on a stand with a horizon-circle, so that its axis can be inclined at pleasure to the plane of the horizon-circle. The inclination may be read on a scale engraved on ring III.

To adjust the apparatus to show the firmament at any appointed place and time, one must place ring III. so that its inclination towards the horizon-circle equals the latitude of the place. Then ring II. must be turned so that its plane coincides with the plane of ring III. The angle between I, and II. must be equal to the obliquity of the ecliptic at the appointed time. Finally, the globe must be turned round the axis which goes through the poles of the ecliptic, till the point of the heaven, which is the celestial pole for the time appointed, comes under the ax.s round which ring II. turns in ring III. If the globe is then fastened in ring I., and ring I. in ring II., with screws, by turning the globe in ring III. one can see at a glance which stars are setting and rising, and which are always above the horizon. By making Vega, for example, the celestial pole (14,000 A.D.),

ROM the behaviour of influenza as an epidemic, it seems not unreasonable to suppose that it may have as its cause a living and multiplying organism; and when influenza reappeared, after an interval of many years, in the latter part of 1889, and more especially since its communicability from person to person, formerly disputed, has come to be generally admitted, the public mind, medical and lay, has been in expectation of the announcement that a specific microbe had been discovered as the cause of the disease.

Even in diseases, however, of which the characters point most strongly to a parasitic microbe as their cause, the discovery of such an organism is by no means an easy matter. Thus, no micro-organism has as yet been identified as the cause of small-pox, although this disease is always more or less with us; breeds true; has distinct characters, and a definite localization on the skin; and propagates by a contagion which retains its activity for very long periods-circumstances which point to a specific organism as its cause, and might be thought to facilitate its discovery.

From a priori considerations we must suppose the properties of the hypothetical influenza microbe to be as follows. The diffusibility of the poison through the air shows that it must be very minute and readily suspended. For the same reason it must belong to the class of aërobic organisms, i e. those for whose existence oxygen is necessary, or at any rate not hurtful. It must multiply with extreme rapidity. It must be capable of multiplying in the bodies, or secretions, of human beings; and probably also in some medium or media outside the human body-perhaps on damp ground-surfaces, or in confined air laden with dust and organic matter. One can hardly suppose it capable of multiplying in pure air, as it would lack pabulum; perhaps, as Dr. Symes Thompson suggests, particles of organic dust floating in the air may serve as rafts for it to live on. As, however, influenza prevails under the most opposite conditions of season, climate, and weather, our supposed microbe, if it can live in the air, must be able to flourish under a great range of temperatures and degrees of humidity. I am not aware of any instances of long retention of contagion, such as would lead us to postulate the possession by our microbe of resting spores. From these considerations we might have expected that it would be more likely to turn out to be a micrococcus than a bacillus.

From what is known of the pathology of some other diseases of microbic origin, as tetanus and diphtheria, it seems possible that the immediate cause of the symptoms of influenza may be the presence in the blood and tissues, not of the microbe itself, but of the poison