April 21, 1910] 



NATURE 



217 



out the forty years the work has been in the hands of 

 students of physics, it has remained the pet child of 

 its creator, and every page bears evidence of the care 

 he bestowed on it. In the work of revision for the 

 present edition, Kohlrausch was assisted by a number 

 of his former pupils, now distinguished for their re- 

 searches in special branches of the subject, so that it 

 em.bodies the experience of the leading physicists in 

 Germany. As an example of a section of the book 

 only possible under a system of collaboration of this 

 kind, that on radio-activity, by Prof. E. Dorn, may be 

 mentioned as of special value. As a result, we have 

 a book thoroughly up-to-date, which, as a work of 

 reference for the physical laboratory, stands in a 

 unique position, both on account of the large amount 

 of valuable matter it contains, and for the completeness 

 of its references. 



In the second place, the author gives us in the pre- 

 face a glimpse at the physical laboratories of Germany 

 fiftv years ago. There were then about two dozen 

 professors of physics', a dozen assistants, and possibly 

 about two dozen senior students engaged in research 

 in the whole of the country, .•\pparatus was scanty, 

 and had to be purchased out of a very meagre annual 

 ^rant. A new professor who could bring- with him 

 his own apparatus, was regarded as a special windfall. 

 Systematic instruction in practical physics was given 

 at Konigsberg, Berlin, and Heidelberg Universities 

 only, but the need for better organisation of the 

 universities in this respect soon became pressing, and 

 was met by the appointment, in the later 'sixties, of a 

 number of professors who had received their practical 

 training in the above laboratories under Neumann, 

 Magnus, and Kirchhoff. The chancre which has come 

 about since then is remarkable. There are now many 

 single laboratories in which a greater number of senior 

 students are engaged in research than were so occu- 

 pied in the whole of the laboratories of the country 

 half a century ago. 



T/ic Schoolmaster's Year-hook and Directory, 1910. 

 A Reference Book of Secondary Education in 

 England and Wales. Pp. lxxi-l-448+700. (London : 

 The Year-book Press, c/o Swan Sonnenschein and 

 Co., Ltd., 1910.) Price 75. 6d. net. 

 This is the eighth annual issue of what has become 

 an indispensable source of information to the educa- 

 tional worker. It consists of three parts, containing 

 respectively general information, alphabetical lists of 

 secondary schoolmasters, and a list of secondary 

 schools. We are able to say from experience that 

 the educational particulars provided by this work are 

 accurate and up-to-date. .Among new features of the 

 book this year are important alterations in the section 

 dealing with county and borough education authorities. 

 It is interesting to note that the directory now con- 

 tains more than 14,000 names, and that the list of 

 secondary schools numbers about 1500. .Altogether, 

 the book deserves a' wide circulation. 



Egypt and the Egyptians. By the Rev. J. O. Bevan. 



Pp. xxii + 224. (London : George Allen, 1909.) 



Price 55. net. 

 This is a compilation of miscellaneous information 

 about " Egypt and the Egyptians, their History, 

 Antiquities, Language, Religion, and Influence over 

 Palestine and Neighbouring Countries," written in old- 

 fashioned style. It has no particular plan, and 

 meanderg about from one subject to another, but 

 not unpleasantly. Sir G. H. Darwin, who disclaims 

 " anything more than the suf)erficial knowledge of 

 Egypt which is open to any hurried tourist," has 

 done Mr. Bevan the honour of writing a preface to 

 his little book, which will no doubt give considerable 

 pleasure, and convey a good deal of information and 

 instruction to many readers. 

 NO. 21 12, VOL. 83] 



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 0/ Nature. 

 Nu notice is taken of anonymous communications.] 



The Term " Radian " in Trigonometry. 



Dr. Thomas Muir, in his letter in Nature of .April 7 

 (p. 156), corrects the misapprehension implied in the " New 

 English Dictionary," viz. the supposition that the word 

 " radian " was first introduced in the " Treatise on Natural 

 Philosophy " by Thomson and Tait. 



Dr. Sluir says he used the word in 1869 in St. Andrews, 

 and goes on to say that it was after conversation with 

 my father, the late Prof. James Thomson, in Glasgow, that 

 the word was finally adopted in 1874. 



I should like to point out that my father adopted the 

 word some years before he came to Glasgow and before 

 he met Dr. Muir. I have a memorandum in my father's 

 writing saying that this name was proposed by him in 

 July, 1871, and it appears in the printed examination 

 questions set by him in the general class examination in 

 Queen's College, Belfast, on June 5, 1873, and published, 

 I believe, in the college calendar. 



I well remember several conversations between my father 

 and Dr. Muir with regard to the use of this and other 

 words, but " radian " had already been adopted publicly 

 by my father, and apparentl}- had been already independ- 

 ently used by Dr. Muir. James Thomson. 



22 Wentworth Place, Newcastle-on-Tyne, April 12. 



The Yfllow Colour in the Stoat's Skin. 



In her letter to Nature of March 24 Miss I. Sollas 

 remarks on the " canary-yellow " colour " in members 

 of the stoat family when the winter whitening is in- 

 complete," adding, "there can thus be little doubt that 

 the yellow body produced artificially in the fur of the 

 albino rat is a substance similar to the yellow pigment 

 of the stoat's winter coat. ..." I do not know whether 

 it has been recorded, though I should have thought so, 

 that a stoat's fur of the purest white will, after exposure 

 to light in a museum case for a time, varying with the 

 intensity of the light, invariably turn distinctly yellow — 

 fainter, however, than " canary-yellow." I have made 

 no chemical or microscopical examination of fur so 

 yellowed, but the usual reason assigned for the change is 

 the absorption by the hairs of a small amount of fat out 

 of the skin, induced by the light and heat of summer. I 

 understand, also, that ermine kept in a dark chamber or 

 box the temperature of which is high will also turn yellow. 

 Stoats in this part of the country often become white 

 early in the season before any real cold weather has 

 occurred. Henry O. Forbes. 



The Museums, Liverpool, .April 12. 



Transit of Halley's Comet across Venus and the 

 Earth in May. 



I beg to direct attention to the following : — 



It is my intention, at Kaafjord, in Finmarken (in the 

 north of Norway), together with my assistant, Mr. O. 

 Krogness, to take magnetic and atmospheric observations 

 during the period May 7 to June i next in connection 

 with the transit of Halley's comet across the sun's disc 

 on May 18-19. 



It is conceivable that the tail of the comet may consist 

 chiefly of electrical corpuscular rays ; and, if this be so, 

 we should expect that these rays, owing to earth- 

 magnetism, would be drawn in, in the Polar regions, in 

 zones analogous with the aurora zones, assuming the tail 

 of the comet to be of sufficient length to reach the earth. 



These rays will then, in such a case, exercise, amongst 

 other things, magnetic influences and electric inductionary 

 effects, especially strong in the Polar regions, and it is 

 particularly such effects we are desirous of tracing. The 

 tail of the comet, if it should consist, as above assumed, of 

 such radiant matter, will alter its shape at a very con- 

 siderable distance from the earth, and we may expect to 



