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Mr. F. SHILLINGTON SCALES, B.A., F.R.M.S. (Microscopical Editor of Knowledge and Scientific News), says in the July issue of that Journal :

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A TEXT-BOOK OF OPTICS. Physical Optics. By R. W. Wood. Pp. xiii+546. (London: Macmillan and Co., Ltd., 1906.) Price 155. net.

WHEN a book on optics by Prof. Wood was

announced, students expected something interesting, and they have not been disappointed. In his preface the author explains that when he commenced his work Preston's "Theory of Light" was the only advanced English text-book of modern date available. Since that time Schuster's "Theory of Optics" and the English translation of the late Prof. Drude's "Lehrbuch der Optik " have appeared, and Prof. Wood had to consider whether they covered the field sufficiently.

His readers have cause to be glad that he answered this inquiry in the negative, nor will they regret the fact that he has laid special stress on the experimental side of the question, and has devoted considerable space to the account of some of his own work. His apologies for this are unnecessary; many of the experiments so described are beautiful, and students learn more from reading a man's account of his own work than in other ways.

While the book hardly claims, perhaps, to be a complete treatise, it covers a great deal of ground, and in particular deals with a number of matters, such as the laws of radiation, dispersion, fluorescence, and the optics of moving media, which are not so fully treated in some other recent works. A student commencing the study of optics would perhaps hardly begin with this book; he would find, however, in its pages when he came to read them some most instructive views of the subject. The earlier chapters deal with the rectilinear propagation of light and its reflection and refraction. They gain much by the photographic reproductions showing the passage of a wave of sound through an aperture, and after reflection and refraction at a plane surface, and teachers will do well to insist on the utility of the graphic method of studying the changes in wave form, which Prof. Wood uses freely.

The theoretical treatment of the matter is perhaps less satisfactory; it is based essentially on that of Verdet. Schuster's paper on the method of analysing in an elementary manner the propagation of a plane wave might with advantage have been alluded to. In dealing with both reflection and refraction, Fermat's law of minimum time is explained at an early stage, and afterwards freely utilised.

A special point in these early chapters is made of the refraction of light by media of varying density, and the results are used to illustrate and explain the phenomena of mirage. Prof. Wood's arrangement for producing mirage on the lecture table is well worth notice; so too are the experiments on anomalous dispersion, and especially the very beautiful one for showing the anomalous dispersion of sodium vapour. We come next to the interference of light. The

usual elementary account of the phenomena shown by Fresnel's mirrors and by the biprism is given, but it is supplemented with a simple description of how to make a pair of very satisfactory mirrors from a piece of modern mirror glass, or a biprism from some slips of glass and Canada balsam, and we are told that "a prism made in this way works quite as well as those supplied by opticians."

After a reference to the phenomena of light beats and achromatic fringes we pass on to the colours of thin plates and Newton's rings. The section on the polarised fringes produced by two streams polarised at right angles is very interesting, so too is that on the preparation of films for the exhibition of Newton's colours.

Diffraction is treated at first in an elementary way, then by means of Cornu's spiral, and finally, for a few simple cases, by means of calculation; the sections on the grating may be specially commended. In chapter viii. we find an able discussion of the modern interference spectroscopes, and here again, both in the case of the Michelson interferometer and of the echelon grating, the experimental conditions for successful working are carefully discussed. The interferometers of Fabry and Perot, and also of Lummer and Gehrke, are also described. The chapter on double refraction proceeds on ordinary lines. Stokes's verification of Huyghens's law might with advantage have replaced that due to Malus, which cannot give results of great accuracy. In chapter xii., the theory of reflection and refraction, the reader is introduced to Maxwell's equations of the electromagnetic field, which henceforth become his main guide in the theoretical part of the book, though the theory of dispersion is in the first instance developed on the lines of the work of Sellmeirr and Helmholtz.

With regard to optical theories generally, Prof. Wood has from the first adopted the view put forward by Schuster in the preface to his recent book on optics.

"So long as the character of the displacements which constitute the waves remains undefined we cannot pretend to have established light." a theory of


In dealing with the theory of reflection and refraction, the importance of the part played by surface films is duly noted. From this point onwards the interest of the book becomes greatly increased. admirable account is given of recent work, much of it due to the author, connected with dispersion and absorption, especially the anomalous dispersion of sodium vapour. The optical properties of metals are developed on the electromagnetic theory, and reference is made to the important work by Rubens and Hagen, who showed that many of the discrepancies between theory and experiment noted by other observers arose from the employment of waves of too short length in the investigation.

After some account of rotatory polarisation, we come to the chapter on magneto-optics. The theory is worked out according to the two lines indicated by Drude; the first hypothesis is based on the existence

of molecular currents in the median streams of revolving electrons the motions of which are acted upon by, and react upon, the magnetic forces of the impressed field, while the second hypothesis is that of the Hall effect, in consequence of which an electron thrown into vibration in a magnetic field experiences a force depending on its own velocity and on the strength of the field. The results of the theory are applied to the discussion of the magneto-optics of sodium vapour, taken from a paper by Prof. Wood himself, and also to an explanation of the Zeeman effect.

Chapters on the laws of radiation, the scattering of light, the nature of white light, and the relative motion of ether and matter conclude the book. In connection with this last subject, Prof. Wood points out that all experimental evidence, with the exception of the well-known Michelson-Morley experiment, is in favour of the hypothesis of a stagnant ether, and that the only explanation of this discrepancy, so far as we can see at present, is that due to Fitzgerald and to Lorentz, that a change is produced in the linear dimensions of matter by its motion through the ether. Sufficient perhaps has been written to show that Prof. Wood has placed students under a considerable debt by the publication of this book, while the publishers are to be congratulated on the manner in which they have produced it.

RESEARCHES IN JAPANESE WATERS. Ostasienfahrt: Erlebnisse und Beobachtungen eines Naturforschers in China, Japan, und Ceylon. By Dr. Franz Doflein. Pp. xiii+511. (Leipzig: Teubner, 1906.) Price 13 marks.


R. DOFLEIN adds one more to the long list of books which have been written to give popular accounts of scientific expeditions. In the year 1904 he undertook a journey to the Far East for zoological purposes, and particularly with the object of investigating the fauna of Japanese waters, which is of peculiar interest, not only as possessing remarkable forms of its own, but as containing an admixture of genera belonging respectively to the cold northern seas and to the Indo-Pacific region, which meet in that locality, with a large "deep-sea " element. In the book before us we have a record of the observations and results of this voyage, and of the impressions made on the traveller by the countries he passed through.

The outward passage was an eventful one. In the Red Sea the Prinz Heinrich, on which Dr. Doflein had left Naples, was stopped and searched by the notorious Russian auxiliary cruiser Smolensk, and the mails were taken from her. The incident was made more exciting by the presence on board of high Chinese and Japanese officials, and created considerable commotion in Europe at the time. Further trouble, however, awaited the Prinz Heinrich. Off Dondra Head, in a heavy sea which would probably have sunk her boats if they had been launched, she

struck some unseen object, sprang a leak, and only reached Galle Harbour just in time to escape sinking. Her passengers were then transferred to the Polynesien, on which they continued their voyage from Colombo, and arrived, after a further mishap in the shape of a breakdown of the engines, at Saigon. From this town, with the beauty of which Dr. Doflein was more struck than with its morals, he travelled by Hong Kong, Macao, Canton, and Shanghai, where he heard of the defeat of the Russian fleet and saw the interned Askold in dock, to Nagasaki, and thence by Yokohama and Tokio to Sendai Bay, in the Rikuzen district on the east coast, where his work was to begin.

The reason which had led Dr. Doflein to choose this locality for his investigations was that on the east coast of Japan the warm current known as the Kuro Siwo, or Japan coast current, derived from the north equatorial drift, meets the cold Kurile current from the north on more or less equal terms, and that therefore in this region the relations of the IndoPacific and northern faunas might best be studied. On the western side of the islands the Tsushima current, an offshoot of the Kuro Siwo, appears to have little influence on the temperature of the water, which, so far as is known, has here a more predominantly subarctic fauna. The result of the investigations at Sendai was to show that there is no sharp boundary between the southern and northern faunas, and there is evidence that the change from the one to the other is gradual, and takes place all along the east coast of Japan. This is probably due to the fact that the two currents interlace in a com

plicated manner and change their position with the

time of year. Our knowledge of these currents is largely owing to the work of the unfortunate Admiral Makaroff, who perished off Port Arthur. Dr. Doflein's stay in Sendai was brought to an end by bad weather, and he then left for Sagami Bay in the south, where he made his headquarters at Aburatsubo in a small marine laboratory belonging to the University of Tokio.

The fauna of Sagami Bay is extraordinarily rich, probably on account of the abundant food supply owing to the mortality among the surface organisms of the two currents in consequence of the change of temperature when they meet. It has been collected by many naturalists from von Siebold onwards, and Dr. Doflein wisely gave his chief attention not so much to collection as to the observation of the habits and mutual interdependence of the animals, both of the deep and shallow waters. He describes his impressions of the latter in a graphic chapter, and makes some interesting remarks on the meaning of their coloration. There seems to be a large tropical element, brought, no doubt, by the Kuro Siwo. After some weeks' investigation of the shallow-water fauna, Dr. Doflein returned to Tokio to hire a small steamer for deep-water work. The first vessel that he chartered sank off Misaki, near Aburatsubo, and thus wasted precious weeks of fine weather, but with another he was able to do good work, both on the

plankton and on the ground-fauna at various depths down to about 900 fathoms. Much material was also obtained for him by Japanese deep-sea fishermen with "Dabo " lines.

In summer the warm Kuro Siwo waters cover the surface of Sagami Bay, but in winter the north-west winds bring down the cold current to overlie it, so that the self-registering thermometers reveal a layer of warm water between two cold layers. In this warm layer the fauna of the Kuro Siwo is found, while the surface layer has a very different and largely getable plankton. As has been said, there is great mortality among both these sets of organisms, with the result that the ground-fauna at all depths, from ide-marks downwards, is extraordinarily rich. The broken nature of the sea-bottom, providing a greatly increased surface and variety of habitat, no doubt contributes to the same result. Another peculiarity of the fauna of Sagami Bay is the appearance in very moderate depths, of sometimes as little as fifty fathoms, of forms which have usually been found Considerably lower, at 500 fathoms to 1500 fathoms. Doflein accounts for this partly by the suitably low bottom temperature, but more by the stillness of the water. Many of the so-called deep-sea forms are, he says, more properly still-water forms, specially adapted to absence of motion rather than to the other peculiar Conditions of the deep sea, and their vertical range would probably be found to be considerably greater were the same attention to be paid to the exploration of intermediate depths that has been given to the investigation of the shore-belt and the deep sea. This surmise appears extremely plausible.

Bad weather and accidents to his apparatus brought the investigations once more to a standstill, and Dr. Doflein left Japan. On his way home he stayed in Ceylon, and he gives an interesting account of his researches on fungus-growing termites there. Some remarks on the spinning ant Ecophylla bring the book to a close. We have read it with great pleasure. The scientific portions are in places very suggestive, the chapters on the ways and customs of various countries, and especially of Japan, are bright and attractive, and the numerous illustrations are often really beautiful. L. A. B.

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intention of his handbook is to supply as plain and simple a means as possible for the identification of those birds, and their nests and eggs, which are to be met with in the inland districts of this country, and are therefore more likely to cross the path of the greater number of persons interested in bird life. Knowing his birds thoroughly well, the author has written most charming and interesting accounts of them, and his long experience of them in the field has enabled him to introduce into his sketches much of the individual character and temperament of each species-those little peculiarities a knowledge of which is only to be gained by long acquaintance, and by which the old hand knows his birds at a glance or by a note heard in the distance. When the object is to teach the beginner in the study this intimate knowledge is very necessary, and all birdmen (who will read the book for the pleasure it will give them) will recognise and appreciate the happy touches of description which arise from it.

As the book will, we think, be in some demand, we offer a few suggestions in view of another edition. To give the salient features of the general appearance of a bird as seen at a little distance should not be difficult, but the descriptions here, in many cases, seem to be hardly sufficient. The fieldfare, for instance, is merely differentiated from the missel thrush (in plumage) as having a more distinct grey patch on the lower part of the back; whereas its greyish head, rich brown mantle, and the blue-grey of the patch on its lower back (from which the bird is sometimes called the "pigeon" felt) might have been pointed out as sufficiently apparent to serve as identification marks. The short wings of the sparrowhawk might have been alluded to, as well as the want in the cirl bunting of the bright chestnut rump so conspicuous in the yellow hammer; the distinctly colder tints easily seen in life of the marsh compared with those of the reed warbler, and the streaked under parts of the adult Montagu's harrier are merely further instances of the kind of recognition marks we wish to indicate.

As the book is intended for readers whose knowledge of ornithology is of an elementary character, something more about the plumage of the chaffinch than the statement that the hen bird is a good deal duller than the cock is desirable, and the want of it is all the more felt, because the following species, the brambling, is said rather closely to resemble the chaffinch, and is described in comparison with it. The whitethroat is described as if it were uniformly coloured on the upper parts, whereas the greyish head contrasts with its rufous-brown back; and as we are dealing with birds seen at a little distance, it would have given a better idea of the cock stonechat to say that he had a black head than that he had a conspicuous black patch on the throat and face. We should not have said that the pied flycatcher had the appearance of being of slender build, nor can we detect that the eggs of the whinchat are usually a good deal greener and deeper in tint than ordinary hedge-sparrows' eggs. The author thinks

that the notion that the mistletoe thrush haunted apple trees for the sake of eating mistletoe berries, and hence got its name, is not confirmed by the bird's actual habits; but we have it on the authority of our greatest living ornithologist (an opinion based on personal observations) that the connection of the bird with the mistletoe is no figment, as some have tried to maintain, and that this thrush is exceedingly fond of the luscious viscid berries of the mistletoe.

While fully allowing that the attempt to put a bird's note into syllables is in most cases a failure (so far as people in general are concerned), there are exceptions, and it would surely have been desirable in the interests of the young field ornithologist to give in words as many of the more remarkable bird-notes as lend themselves to this treatment. The "you-tick" of the whinchat and the "twit me-dick " of the quail (from which the birds take local names), the "hweet-tittit" of the redstart and the "chuck-chucka" of the red-legged partridge, are a few cases in point. But to take the case of the curlew as here treated, no mention is made of the fact that some of its varied cries have suggested names for it, and the remark that "the cry recalls some of the notes of the plover, but is far more free and powerful," hardly seems to convey an adequate idea of the curlew's characteristic cries. We wonder if the song of the lesser whitethroat would strike most people as more "quiet and unobtrusive " than that of the whitethroat.

The descriptions of the nests and nesting habits are especially successful, and will be most interesting to experienced bird-nesters, as well as useful to the novice. The coloured figures give, on the whole, a good idea of the eggs, although some of the plates suggest threecolour printing, and that one colour has obtained undue prominence. White eggs are merely figured in outline, and the artist has succeeded in representing the characteristic shape of average specimens. An index, which is all that can be desired, and a classified list of breeding species and regular visitors make reference to the different species easy; but we cannot understand the application of the note to the latter, that the visitors are distinguished by italics, for we find very few names so treated, and among them those of both the yellow and the grey wagtails.

Mr. Elms's thin volume, which slides so easily into the pocket that there is no excuse for leaving it behind on a field day or omitting to take it out every morning during the migration seasons, is intended solely for the purpose of reference in the field. All our British birds (properly so-called) are included, the rare and accidental visitors or stragglers to our shores hardly coming within the scope of the book, as the chances of seeing them during a country ramble are very slight. A vast amount of information has been included in the small compass of this pocket-book; the plumage, period of residence in this country, language, habits, haunts, and food are all treated concisely under their several headings, as well as some particulars of the nidification; but in the last respect it is pointed out that the present volume is intended to be used and carried in conjunction with the new edition of

Newman's " Bird-nesting and Bird-skinning." which is of the same size and issued by the same publisher and contains full particulars of the nests and eggs Some of the observations on bird language, these on some of the gulls and terns, for instance, do no appear to be altogether satisfactory, but this hand little volume (which is furnished with a good ind cannot fail to be of great service to the student field ornithology.



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Preliminary List of Durham Diptera, wh Analytical Tables. By the Rev. W. J. Winga Transactions of the Natural History Society Northumberland, Durham, and Newcastle-uj« r«Tyne. (New Series.) Vol. xi. Pp. vii+416; wit? seven plates. (London and Edinburgh: Williams and Norgate; Newcastle-upon-Tyne: F. and W Dodsworth, 1906.) Price 9s.

THE author, or, as he would probably prefer to fu

styled, the compiler, of this excellent manu has done himself less than justice, for if, instead the modest title associated with the name of a sing English county, he had chosen some such designation as that at the head of this notice, he would mer accurately have expressed the scope of his work and would also, perchance, have brought the latter to the notice of a wider circle of readers.

Little by little budding entomologists in this country are beginning to realise that butterflies and moto and beetles are not the only orders of insects worthy of study, and the number of those who devote their energies to the flies, or Diptera, though still small b comparison with that of the students of the more popular orders, is steadily increasing. As Mr. Wo gate truly remarks in his preface, no other order o insects has so many interesting and varied lihistories, and none so deeply affects the human race whether as protectors when acting the part ut scavengers, or depredators destroying the crops, ir scourges carrying the deadly micro-parasite." fortunately for the beginner, the bulk of the literature dealing with European Diptera is in foreign tongues, chiefly German, and, Walker's "Insecta Britannic being hopelessly inadequate and out of date, it has hitherto been impossible to satisfy the natural deman of the novice for a work in English that, while supo'y ing an outline of the structure and classification of Diptera, will at the same time provide the means for the identification of the bulk of the British represen atives of the order. The basis for all work upe British Diptera is, of course, Verrall's "List," t second edition of which was published in 1901. In this are the names of 2884 species, and when it added that Mr. Wingate's tables, which are chie1 derived from Schiner's classical work on the Dipter of Austria, furnish characters for the determination of no fewer than 2210 of these, it will be seen that the present volume should go far towards supplying the British student with precisely the aid that he requires. In addition to those already mentioned, details art

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