deavouring to effect a compromise between purely elementary works on astronomy and advanced treatises, it is worthy of some praise. With the many remarkable developments of astronomical science during the last quarter of a century, the bulk of the original volume has been somewhat increased by additions, and it has now been decided henceforth to publish the work in three divisions, viz.

(1) The sun, planets, and comets.

(2) Instruments and practical astronomy. (3) The starry heavens.

The first division of the work is now before us, and viewed as a handy book of reference it has many commendable features; but all that could be said in its praise would be the reiteration of comments upon former

editions.

The most important application of spectroscopy to astronomy is too well known to need any enlarging upon. It may be said to be almost entirely a creature of the last quarter of a century, but by far the greater amount of this spectroscopic work has been directed to the sun, whilst many new and important discoveries have been made in connection with it. In pre-spectroscopic times a spot on the sun was only that, and nothing more; and a solar prominence was a stupendous flame, the observation of which was only possible at eclipses. Nothing was known of their constitution; and, in fact, all we now know of the physical and chemical condition of the sun has been gained by spectroscopists. However, it is not necessary here to consider the enormous work that has been done in this direction, but it is our duty most emphatically to protest against a compilation such as the one before us-purporting to be a completely revised account of astronomical labours and advances, and yet rendering terribly conspicuous by its absence everything that relates to spectroscopy. It is like a book on loco

motion leaving out all about railways because they were not prominent when the first edition was published. The pictorial representations of the corona, the solar prominences, the surface of the sun and the spots upon it, are well discussed in their respective sections, but no room has been given to an examination of their constitution by means of the spectroscope; and indeed, as far as this book is concerned, the whole work that has been done in connection with solar physics might have been left undone.

But these remarks apply not only to the chapters relating to the sun; those on the planets and comets respectively are in the same incomplete condition. Without the spectroscope, the source of luminosity of a comet was far beyond human ken, and its whole constitution was a matter of considerable doubt; with this instrument, how

aid of the spectroscope, we have been enabled to obtain much new information about its physical constitution The subject being, however, a physical rather than a astronomical one, and involving a great amount of optical and chemical details, it cannot conveniently be discusse. at length in a purely astronomical treatise, though some thing will be said concerning it later on in the portion o this work dedicated to spectroscopic matters."

This explanation, however, only aggravates the fault The importance of the work that has been done is asented to, but, instead of including that part of it relatin, to the sun in a chapter on that body, instead of consider ing the spectroscopy of comets as inseparable from chapter devoted to their discussion, the author has rele gated the whole work to an unpublished section devoted to astronomical instruments. Such an arrangement is undoubtedly wrong. A chapter on the sun must contain all that is known about that body, if it strives to be at all complete; similarly, a chapter on comets cannot approach completion unless their spectra are considered; thus this work cannot lead the general public to a just appreciation of the many advancements that have been made. The most elementary text-books rightly include the spectroscopic labours and discoveries, whereas this so-called hand-book. although aiming at being an historical account of the work that has been directed to the sun, planets, and comets respectively, leaves a vast array of facts out of consideration altogether.

There are a few minor faults, one of which is the figure relating to Foucault's pendulum experiment for determining the rotation of the earth. The author ap pears to have discarded the method of suspension adopted by Foucault, and the pendulum is sketched as if rigidly attached to a beam. The accompanying tex also leaves this most important experimental detail out of consideration.

But apart from these points, the work is worthy of some commendation. An addition has been made to the chapter on comets, viz. a method of determining the elements of the orbit of a comet by a graphical process. The catalogue of comets whose orbits have been com puted has also been brought up to date, and similar additions have been made to the chapters on periodic and remarkable comets. Doubtless the book will prove to be what it has been heretofore-a handy reference to some astronomical facts.

ELECTRICAL UNDERTAKINGS. Proceedings of the National Electric Light Association at its Ninth Convention, 1889. Vol. VI. (Bostor. Mass., U.S.: Press of Modern Light and Heat, 1884)

light has been analyzed, and the whole sequence of changes, as it goes from aphelion to perihelion and back again, is now understood. Yet the spectroscope might never have been turned to these bodies, or indeed utilized in any way, if the utility and importance of the work done were measured by the brief notice with which the author has seen fit to dispose of it, and the following may be said to be the reason for his grievous omissions :—

"The study of the sun has during the last few years taken a remarkable start, owing to the fact that, by the

proceedings of the National Electric Light Association in the United States during the Convention he at Chicago on certain days in February 1889.

This body is one which, in the United States, has been brought into existence by the growing necessities and rapid expansion of the electric light and power industry Probably its nearest English analogue is the Iron and Steel Institute. It is essentially a commercial associa tion, and its aims may be said to be comprised withir the limits of the exchange of practical information

monographed by De Candolle in the "Prodromus " between 1824 and 1830, and the scattered material relating to many of the orders and genera has not since been brought together and codified. As instances of genera now involved in great confusion for want of a more recent elaboration, we may cite Ranunculus, Viola, Papaver, Alyssum, Draba, Dianthus, Geranium, Galium, and many others. The present paper is, unfortunately, not a monograph of Dianthus, but only a list of the known species classified into groups, accompanied by general remarks on the structure of the different organs in the genus, and on their range of variation, so that, though it is interesting and useful as far as it goes, it still leaves very much to be desired. Although, on the one hand, Caryophyllacea are dried for the herbarium very easily, and suffer little in the process, yet Dianthus is a very difficult genus for botanists to deal with and to understand. There are 230 species for a monographer to characterize. The range of variation between the extreme types is not great, and some of the commoner species (e.g. D. Seguieri, plumarius, and Carthusian orum) are very variable, the consequence being that, one often sees them named in gardens very incorrectly, forms of plumarius especially, which is hardy and spreads readily, doing duty for many totally distinct species.

Dianthus is a genus quite characteristic of temperate and sub-temperate climates. It has its head-quarters in Europe and Western Asia. There are several species at the Cape; a few are Himalayan, Chinese, and Japanese; none reach Australia, New Zealand, or the Andes; and only one just touches the extreme north-western tip of the American continent. There are two principal sub-genera: Caryophyllastrum, of which the carnation may be taken as the type, which is far the largest ; and Armeriastrum, or Carthusianastrum, of which the flowers are numerous and clustered, as in the sweet-william. There is a third small sub-genus, intermediate between Tunica and the true pinks, which is classified by Bentham and Hooker with Tunica, and by Mr. Williams, following Linnæus and Koch, as a third sub-genus of Dianthus. Within the bounds of the genus, Mr. Williams finds his primary characters-those which mark groups-in the form of the calyx, the nature of the margin of the lamina of the petals, the presence or absence of a beard at the junction of the blade and claw of the petals, filaments, and styles, the shape of the leaf, and the disposition of the flowers; and his secondary characters-those which distinguish species in the number and shape of the bracts of the epicalyx, the form of the lamina of the petals and their apposition, the character of the calyx-teeth, the form and structure of the capsule, the form and structure of the seeds, and the disposition of the fascicles of veins in the leaves of the barren shoots and flowering stems. His groups and species do not differ materially from those given in his paper in the Journal of Botany for 1885, p. 340. The list would have been more useful if he had stated the native country of each species, and added a reference to where it was first described. We hope, however, that he will see his way to publish, before long, the monograph of which this is a mere outline sketch. J. G. B.

OUR BOOK SHELF.

Magnetism and Electricity. By Arthur W. Poyser, M.A (London: Longmans, Green, and Co., 1889.) SINCE the amount of knowledge that is supposed to coastitute an elementary scientific education increases ever. year, there is sufficient justification for the publication of a series of science manuals designed to meet the growing requirements of the Science and Art Department examin tions, and this work is an excellent representation of such a series. Apart, however, from the value of this book as an examination manual, it possesses considerabi merit. The matter contained in it is just about as much as would cover the course usually taken in a year clearest language, and the experiments described are school work; the explanatory text is couched in the capable of being easily brought to a successful termination. Also the 235 illustrations will be of considerable assistance to the student, whilst the many exercises and examination questions interspersed throughout the book may be useful tests of his knowledge. The text-books that in their day have been eminently successful, if un revised, must be supplanted by others which take a more extended view of the subject; hence it is that this book will compare most favourably with any written for the purpose of imparting a rudimentary knowledge of magnetic and electrical phenomena and the laws by which they are governed.

The Engineer's Sketch-book. By Thomas Walter Barber (London: E. and F. N. Spon, 1889.)

The

ENGINEERS and draughtsmen generally keep note-books in which are jotted down most things they wish to particularly remember, accompanied by rough sketches when necessary. The author of this book is no excep tion to the rule. He tells us he has made many notes and sketches during his experience as an engineer, and has often found the want of such a collection for refer ence. This volume consists of about 1936 sketches, classified under different headings, of devices, appli ances, and contrivances of mechanical movements. book is certainly unique in its way, and will prove usef to those who have machinery to design, who may require suggestive sketches of mechanical combinations to ac complish some desired end. The author truly remarks that a sketch properly executed is to a practical man worth a folio of description. Hence the descriptions gives are generally mere names, with occasionally a concise statement of purpose. Each sketch bears a number, and on the opposite page this number is to be found with the description, &c.,-a very good arrangement.

These sketches are clearly printed, and are probably executed from scale drawings in most cases. Taken as a Sketch 1636, however, is supposed to represent a Ramswhole, they fairly represent what they profess to do bottom safety valve, but it gives a radically wrong im pression of this valve. The lever is shown resting on the two valves certainly, but the spring is attached to the lever at a point considerably above the assumed straight line joining the points resting on the valves-an impossible position. Again, one of the two points of the leve resting on the valves is usually loose and connected with the lever by a pin. The sketch shows the lever and the two projecting points made solid. This example is the most unpractical sketch discovered in the book, and should be rectified in a future edition. A fairly good index adds to the usefulness of the volume. There is ample evidence of careful work on the part of the author, and he is to be congratulated on writing a book which will probably be of use to many engineers and those connected with the profession. N. J. L.

A Life of John Davis. By Clements R. Markham, C.B., F.R.S. (London: George Philip and Son, 1889.) THIS is the first volume of what promises to be a series of great value and interest. The object of the series, as explained by the editors, is to provide a biographical history of geographical discovery. Each of the great men who "have dared to force their way into the unknown, and so unveiled to us the face of mother earth," will form the subject of a volume; and an attempt will be made, not only to present a vivid picture of the character and adventures of these heroes, but to estimate exactly the scientific value of their work. If the scheme is carried out in a manner worthy of the stirring tales to which it relates, the series will be a source of much wholesome pleasure to all who care to understand how our present knowledge of the earth's surface came to be built up, and who are capable of appreciating the splendid qualities, moral and intellectual, of all who have won for themselves a place in the list of illustrious explorers. The subject of the present volume could not have been intrasted to a more suitable writer than Mr. Clements Markham. He tells in a simple and natural style the le of Davis's life, displaying at every stage of the story f.ll and accurate knowledge, and summing up clearly the achievements which entitle the discoverer of Davis Straits to be ranked "among the foremost sea-worthies of the glorious reign of Queen Elizabeth." Two admirable chapters are devoted to the following-up of the work of Davis, and in an appendix the author gives all necessary information as to authorities. Mr. Markham has done his work well, and it will be no easy task for the writers of the succeeding volumes to maintain the series at the same high level.

The Brook and its Banks. By the Rev. J. G. Wood. (London: The Religious Tract Society, 1889.)

The Zoo. Second Series. By the Rev. J. G. Wood, London Society for Promoting Christian Knowledge, 1889)

THE first of these two books was written for the Girls'

Un Paper, and a few chapters of it have been printed in that periodical. Now the complete work is issued separately, and it will no doubt be welcomed by many readers who have already profited by the late author's well-known writings. The reader is supposed to be conducted along the banks of an English brook, and to learn, as he advances, the characteristics of the living creatures which are to be found by the way. The idea is carried out brightly, and-we need scarcely say-with ample knowledge. There are many illustrations, and they add considerably to the interest of the text.

"The Zoo" contains an account of animals of the weasel tribe, the seal tribe, the rodent family, and various kinds of oxen. The descriptions are clear, compact, and lively, and cannot fail to interest the young readers for whose benefit the book was originally planned.

Mr. Harrison Weir contributes a number of excellent illustrations.

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.]

Protective Coloration of Eggs.

THE following letter records a very interesting observation which is new to me, and I should be glad to hear if any similar fact has been noted lefore. If not, it would be very interesting

"Merchant Taylors' School, Crosby, Liverpool, October 15, 1889.

"DEAR SIR,-I wish to bring before your notice an observation of mine relative to the purpose of colour in animals.

The red-backed shrike (Lanius collurio). Colour of eggseither pale blue or green, white ground with zone of spots at larger end; or, pink ground with reddish spots.

Observation. The colour of the lining substance of the nest-such as roots-assimilates to the colour of the eggs, being dirty gray material when the eggs are to be pale (blue or green) white, but being of red-brown roots, &c., when the eggs are to be pink.

"Evidence for above statement. About sixteen years ago I was a lad of fifteen, an enthusiastic birds'-nester, living at Maidstone, and found several (I forget how many) nests, and noticed this; and it so puzzled me-because I could not make out how the bird knew what coloured lining to select, because she made her nest before she laid her eggs-that I have never forgotten it. In those days I had never heard of The Origin of Species,' nor did I trouble myself about evolutionary theories, knowing nothing about them, so that there was no predisposing cause in me to make a wrong observation. Yet I remember it was only a school-boy's observation, and therefore it needs confirmation. "Assume the fact. Protective, obviously. Yet, how does the bird know? We know birds build nests from observing other nests, and not by instinct wholly.

(a) Have we here incipient species, in which the young, emerging from pink eggs, remen.ber their own infancy in a reddish nest?

"(b) Has the sight of the red lining an influence over the mother to tinge the eggs pink-i.e. would a shrike brought up in a pink cage be more likely to lay pink eggs? or a gray rabbit in a black or white hutch have a greater proportion of black or white variants in her litter?

"(c) A mere coincidence; too few observations.

"Will you forgive one who intends to be amongst your audience on October 29 and 30, if not prevented, thus trespassing on your time-time which, spent in research, is so valuable to vation is worth recording, if only to direct other observers. the whole scientific world? Yet, I do think my boyhood's obser

66

'E.g. has the amount of white quartzite veins in a cliff, or chalk, any influence in the percentage of white, as against blue, eggs of the common guillemot ?

"Believe me, yours faithfully,

"(Rev.) FRED. F. GRENSTED."

Science and the India Civil Service Examinations. THE position of science candidates in the Civil Service competitions is largely in the hands of the science examiners. In some cases they have practically struck their subject out of the schedule by requiring, or by acquiescing in, the demand for a standard of knowledge far beyond the proportion of marks assigned. Even in the last India Civil Service competition the

first two men in chemistry only scored 196 and 195 respectively, whilst the first two in German, out of the same maximum, gained 359 and 353. If the eminent men of science who undertake these examinations would see that science had fair play, many more candidates would be encouraged to study it. Whatever the private views of the Civil Service Commissioners may be, their absolute justice and honourable impartiality are unassailable. Even if they did not altogether concur in the opinions of the examiners, they would give their arguments careful consideration, and see that all interests should be duly regarded.

It will not advance the claims of science to weight them with the very doubtful proposition that "the Universities of England and India" are the only places where "well educated" men are to be found. Many most distinguished men of science have not had the advantage of a University degree in early life. No one would venture to class them for this reason in "an inferior order of men." HENRY PALIN GURNEY.

2 Powis Square, W., November 15.

The Physics of the Sub-oceanic Crust.

IN the new edition of his "Physics of the Earth's Crust," Mr. Fisher has made a great advance on his former position, for he sees his way to explain the formation of mountain chains, and all the phenomena of compression which are so strikingly exhibited in the crust of the earth, without depending on his former theory of columnar expansion, and without falling back on the contraction hypothesis.

He believes that the existence of a liquid substratum beneath a thin crust is consistent with the physical conditions of the universe; and argues that no appreciable tide would be produced in it if the liquid magma consisted of an intimate association of fused rock and dissolved gases. He further concludes that this magma is not an inert or motionless liquid, but one in which convection currents are constantly bringing up heat from below, and leading to frequent internal displacements of mass.

In this hypothesis he finds a means of explaining the movements of the earth's crust. Whether Mr. Fisher's position can be maintained must be decided by those who are accustomed to deal with the physical problems involved, but geologists will be glad if it should prove that the objections to the existence of a liquid substratum have been succes-fully met, for they have always found a difficulty in explaining geological phenomena without having recourse to the supposition of a liquid layer.

One of the most important chapters in the book is that on the sub-oceanic crust, and it is on this that I propose to offer a few remarks, taking it for granted that a truly liquid substratum with a play of convection currents does really exist.

Mr. Fisher's object is to ascertain the thickness and density of those parts of the crust which lie beneath the oceans, and to see whether in these respects they differ from the continental portions. This he does by making a series of assumptions, and considering how far the results are compatible with known facts and conditions. This process involves the dismissal of certain hypotheses, but although he eventually finds one which fulfils the requisite conditions, it does not follow that no other equally satisfactory hypothesis can be found. Consequently his results though interesting cannot be regarded as final. The suppositions he is obliged to introduce before obtaining satisfactory results are, that the density of the subtratum beneath the continental and the sub-oceanic portions of the crust is different, and that the sub-oceanic crust consists of two layers of different densities.

It is conceivable, however, that the lower part of the crust is everywhere denser than the upper part, and consequently that two layers of continental crust should be introduced into the problem; whether this hypothesis would likewise fulfil the conditions, and whether it would lead to the same results as that which Mr. Fisher adopts, could only be ascertained by trial. Mr. Fisher informs me that he has not made this trial, and that every additional assumption introduced increases the great labour of the calculations.

Let us assume, however, that no other hypothesis would satisfy the conditions so well as that which he has adopted, and let us see to what conclusions it leads. Mr. Fisher derives from it the following important results :

(1) That the sub-oceanic crust dips more deeply into the substratum than the continental crust.

(2) That its lower part is more dense than the substratum. (3) That the density of the liquid substratum is less beneath the oceans than beneath the continents.

This last result leads to the conclusion that the differences of density in the substratum must give rise to ascending and descending convection currents, and that the ascending currents will rise beneath the oceans while the descending currents will occur beneath the continents. "That the former occupy so much larger an area is," he says, "no more than we might expect, because to whatever immediate cause they may be due, they are ultimately the result of secular cooling. . . . The descending being merely return currents will be confined to the smaller area, but on that account they will move the more rapidly.'

Finally he says that these conclusions confirm the theory of the permanence of oceans, "because it is difficult to conceive how the subjacent crust, once more dense, can have subsequently passed into the less dense condition which would be requisite to render it continental." I venture to think he is hardly justified in making this unqualified statement, and purpose to show that his results only confirm the theory of the permanence of oceans in a limited and partial manner.

In the first place, if chapters xvii. and xxiv. are read carefully,

it will be obvious that Mr. Fisher uses the terms oceanic and ** oceanic in a special sense. On p. 233 he classes areas having than two vertical miles of water as "extensions of the elevat that produced the continents," and even those with depths of • to three miles of water he regards as "sometimes connected wi and prolongations of the first." In other words, he looks 05 the shallower parts of the great oceans from a continental ca line to a depth of at least 2000 fathoms as extensions of continental elevations.

Again, on p. 331 we find him saying that New Caledonia the Seychelles are not properly speaking oceanic islands, bec the first is a prolongation of the submerged ridge which coune.. New Zealand with North Australia, and because the late belongs to an extension of the Madagascar ridge into the Ing. Ocean. Now a reference to the physical chart of the our given in the " Narrative of the Cruise of the Challen ̧r (vol. i.) shows that the 1000-fathom line completely encirce New Caledonia and the adjacent islands, and that the submeryridge which he speaks of would be a very narrow one unless eregard it as extending to the line of 2000 fathoms ; but this leincludes also the Solomon Islands, the Fijis, and the Frier i Islands, so that if New Caledonia cannot be considered 18. oceanic island neither can the other islands just mentionA though no one would reject them from that category on o grounds. Similarly, the Seychelles and Amirantes are surroundby water of more than 1000 fathoms, and are usually regarded a oceanic islands. The same may be said of Barbados, wher stratified Neozoic rocks are found.

The contour-line of 1000 fathoms has, I think, been generally taken by recent writers as the approximate limit of ta continental elevations, the space outside this being regarded u oceanic; the islands which rise from depths of over 1 fathoms would on this view be necessarily classed as ocean and as a matter of fact all such islands come within the terms of Sir A. Wallace's definition of an oceanic island except that a few of them are not entirely of volcanic or coralline compositor To exclude all the islands which rise from within the 2000-fath= limit would necessitate the division of oceanic islands into two classes, the definition of which would be difficult

I am not saying that such a distinction would be incorrect, in that Mr. Fisher has no right to assign larger limits to the continental elevations and narrower limits to the oceans: Is desire to show that he takes a special view, and that he declines to regard islands which rise from less than 2000 fathoms specimens of the sub-oceanic crust. His discussion of the probable structure of the sub oceanic crust deals therefore wà areas which are covered by water of three miles or more in depththat is to say, from about 2500 to 5000 fathoms, and the comparison which he makes between patches of sub-continent: and sub oceanic crust is really between a piece of continenta land and a piece below an area of deep ocean at a considerable distance from the continents.

With regard to this point, I have had the advantage of a further explanation from Mr. Fisher; writing to me he say "My sub-oceanic patch may be anywhere under the ocean, b you must remember that all the quantities are subject to change except c, p, μ, σ, as & diminishes; i.c. as the ocean grows shallower toward the coast-lines, the thicknesses and densies merge into those at the sea-level, the second layer of the subor oceanic crust at the same time thinning away to nothing. Y are quite right in thinking that in a general way in discussing the sub-oceanic crust I am dealing with the crust at a consider able distance from the continents. . . . . I do not profess to explain the structure of the crust of the earth in those parts wha appear to have sometimes been land and sometimes sea should, however, guess that having been at times land the crust there resembles the present continental crust. equations (p. 242) must apply to these parts if only we knew what assumptions to make."

Still the

Since, therefore, there are regions of sub-oceanic crust ht structure of which may resemble that of the continental cs' rather than that beneath the central parts of the oceans, clearly of importance to consider the position and extent of thes regions. Let us first take that part of the Pacific Ocean in whic New Caledonia is situate; if we are to regard it as a submergel plateau which may once have been continental land, it acquis a special interest. The contour of 2000 fathoms which unite New Caledonia to Australia and New Zealand extends from th north coast of New Guinea by the Solomon Islands to Sams and then bends southward to New Zealand, but curves out aga