4r6 



NA TURE 



[February 28, 1901 



primary groups, here inadvertently termed " orders " and 

 " suborders" {cf. p. 178, where the Sauria are described 

 as a suborder), are set forth, one cannot fail to be struck 

 by the want of logic and of perception of proportions 

 which characterises the new arrangement. It may also 

 be pointed out that the group A?tmellotdea has been 

 omitted from the synopsis ; this is but one out of many 

 clerical oversights of a similar kind which a rapid 

 inspection of the volume reveals. 



A glance at the definitions of the species in the 

 difficult genera, such as Sceloporus and Cneinidophorus, 

 shows that the subject has not been mastered. An 

 attempt to name an extensive series oi Sceloporiwiih^ the aid 

 of the key given would, it can be predicted, result in failure, 

 in the classification of the snakes, the author agrees 

 with the reviewer in the main divisions. The innovations 

 are mainly due to the consideration of the structure of 

 the intermittent organ or " hemipenes " of the male, by 

 the use of which character many changes have been in- 

 troduced in the limits of the genera and in their groupings, 

 changes which are not likely to meet with general 

 acceptance. Far too few species have as yet been tested 

 with regard to this character, and Cope himself admits 

 of occasional exceptions, which have turned up in the 

 course of his investigations, such as when one of the 

 paired organs has proved to belong to a division of his 

 system different from that of its fellow on the same 

 specimen. A priori, it does not seem that the develop- 

 ment of folds and spines on such an organ is at all 

 likely to have so deep a signification as to assist in 

 establishing subfamilies and genera ; to adduce a some- 

 what parallel example, we might as well attempt to 

 employ the differences . in the nuptial excrescences of 

 male Batrachians for the definition of genera and even 

 higher groups. And if we are to judge of the value of 

 the character by the changes which its consideration 

 warrants in the groupings of the genera, its introduction 

 in the system does not appear as anything in the way 

 of an improvement. 



The investigation of the lung characters, to which the 

 author has devoted so much attention, is a more useful 

 piece of work, so far as taxonomy is concerned, and it 

 may be mentioned that through it the view once pro- 

 pounded by the writer of this notice that the Amphis- 

 bsenids may be directly derived from degraded types of 

 Teiids, has proved to be untenable. 



Allusion has been made above to some extraordinary 

 errors which have crept into this work. Two may be 

 mentioned, apropos of snakes, as illustrations : — P. 1127, 

 the Hydrophiinae are stated to " leave the water to deposit 

 their eggs " ; p. 1 129, Eehis carinattts is described as the 

 " Krait " of India. 



The illustrations are numerous and for the most part 

 excellent, and an interesting essay on the geographical 

 distribution of Batrachians and Reptiles concludes this 

 monograph, which, in spite of its imperfections, such as it 

 is a reviewer's duty to point out, will prove of great service 

 to the student of a highly interesting but most difficult 

 group of animals, our knowledge of which has been so 

 greatly advanced by the genius and industry of Prof. 

 Cope. The work is also useful as a catalogue of the 

 specimens preserved in the United States National 

 Museum in Washington. G. A. B. 



NO. 1635, VOL. 63] 



PRACTICAL PHOTOMETRY. 



Photometrical Measurements. By W. M. Stine, Ph.D., 

 Williamson Professor of Engineering, Swarthmore 

 College. Pp. xi + 270. Illustrated. (New York : The 

 Macmillan Company. London : Macmillan and Co. 

 Ltd., 1900.) Price bs. 6d. net. 



AS a " manual for the general practice of photometry, 

 with especial reference to the photometry of arc 

 and incandescent lamps," this work will be found useful. 

 Most of the descriptions of photometers are clear and 

 well illustrated, and much practical information about 

 standards of light is collected together. That strange 

 medley of apparatus etishrined in an expensive taber- 

 nacle of mahogany and velvet called by gas engineers 

 a " photometer " is not even mentioned, possibly because 

 the book is of American origin. Photometers, and those 

 parts of the art of photometry which are of use to 

 engineers, may be defined without much difficulty, and 

 the apparatus and methods suitable for the research 

 laboratory may] be grouped together ; when to these is 

 added the theory of the subject, the whole ground of 

 photometry is covered. But the author makes no such 

 distinctions, and the value of his work suffers. While 

 his reference to spectro-photometry is meagre, and the 

 bolometer is dismissed in less than six lines, he drags in 

 double integration to determine the mean spherical in- 

 tensity of a purely academical case of distribution. On 

 the other hand, he treats possible cases of distribution 

 in a clear and practical way. The description of 

 a Bunsen photometer in the crude form of a screen 

 without mirrors or prisms, and an ancient algebraical 

 theory of the Bunsen screen, containing no reference 

 to the angle of emission or direction of view, marks 

 the author, as do many other passages, as a science, 

 teacher. He is in good company ; there is hardly a 

 text-book of physics in English in which that useless 

 affair is not represented as a Bunsen photometer. In 

 common with most science teachers, he assumes that 

 the shadows of a Rumford photometer must be widely 

 separated, and he very properly alludes to the lack of 

 sensitiveness which results. When Lord Kelvin said 

 that no one could need a better photometer than a pencil 

 and a white card he knew that the edges of the shadows 

 should meet, and, it may be added, that the shadows 

 should completely cover the card. The little-known, 

 but valuable, Conroy, Ritchie and Thompson photometers, 

 varieties of the Rumford, are described, and the somewhat 

 over-rated Lummer-Brodhun apparatus is criticised. To 

 describe the use of the rotating sector without allusion to 

 Abney, the light of the arc without reference to Fleming, 

 S. P. Thompson or Mrs. Ayrton, and measurement of the 

 mean spherical candle power of arcs without reference 

 to Blondel, can hardly be excused by the attempt to 

 compress the whole book into 261 pages. That the 

 author is a professor of engineering may account for the 

 excellence of the practical parts of the manual ; but 

 that, being a professor, some of the theoretical parts 

 are so obscure is strange. 



He must needs allude to " the logarithm of the ratio " 

 in defining Fechner's law, because he is a professor ; he 

 goes on to give a lucid arithmetical example, because he 

 is an engineering professor, but after a page relapse? 



