920 



SCIENCE. 



[N. S. Vol. XIX. No. 494. 



and the size of the images. The ' Dioptrische 

 Uutersuchungen ' ' in words of one syllable ' 

 is hardly attainable, but that of it which is 

 indispensable seems here to have been pre- 

 sented in the simplest possible manner. Sys- 

 tems are compounded and equivalent lenses 

 calculated by the aid of Newton's formula, 

 ' cc' = if',' in which the principal foci of a 

 system are used as coordinates from which 

 conjugate foci are measured by a symmetrical 

 notation. In this way a good working theory 

 is obtained, and is so illustrated by examples 

 chosen from the eye itself, that the student be- 

 comes familiar with the constants with which 

 he will be subsequently concerned. Chapter 

 v., the following, is on ' visual acuity.' From 

 this on the science is not very mucli separated 

 from the useful art by which it is likely to be 

 applied in practise. Most of the subject mat- 

 ter which comes to us by or through Tcherning 

 and Landolt appears here and is in general 

 very well presented. The author does not 

 hesitate to express an opinion of his own oc- 

 casionally. Among other things he says the 

 Morton ophthalmoscope is the best for refrac- 

 tion purposes, from which we judge the hole 

 in the small mirror is made larger than it 

 was in the earlier instruments. The horopter 

 has been robbed of half its interest. This 

 devilish contraption which kept Helmholtz 

 awake nights and which lesser men have 

 dodged as ' un probleme de mathematiques 

 assez complique et sans grand interet ' floats 

 in from somewhere this side of the Rocky 

 Mountains bearing a brand new name and 

 shrunk to nothing more or less than a toric 

 surface. We prefer it with its old euphonious 

 title and complicated contour. 



Near two hundred pages of the book are 

 taken up with normal and abnormal refrac- 

 tion. Included in this part is a chapter on 

 optometers of some historic and theoretic in- 

 terest; also a chapter on retinoscopy well pre- 

 sented. Retinoscopy is a sine qua non to a 

 few men who paralyze all cases and do a rough- 

 and-ready refraction practise among infirmary 

 patients. But retinoscopy is also a necessary 

 part of the modern oculist's equipment and 

 deserves the space here given to it. 



Dr. Gibbons in common with most other 



oculists thinks there is no place in the world 

 for the ' refracting optician.' He does not 

 devote much attention to his natural enemy, 

 but he offers him no quarter. Prom a purely 

 medical standpoint the oculist may have the 

 best of the argument, but the refracting opti- 

 cian is abroad in the land and is not likely to 

 be preached out of existence. There are eco- 

 nomic conditions which contribute to his suc- 

 cess and justify his claim to recognition. 



It is of course quite proper that the author 

 should give a list of cycloplegics and their 

 peculiarities and the method of procedure to 

 be adopted by those who habitually use them 

 in the fitting of glasses. The number of such 

 is so great that they can not be ignored, but 

 why so many oculists still think it worth while 

 to acquire the useless and irrelevant informa- 

 tion that comes from fitting glasses to a 

 paralyzed eye is hard to tell. It may be 

 gathered from the text that the author thinks 

 such a course should be the rule rather than 

 the exception. 



In the line of petty fault finding it might 

 be said that Holmgren's color test is rather 

 meagerly given, that the description of a 

 Rochon prism is made to do duty for a WoUas- 

 ton, that it is a little dogmatic to assert in an 

 unqualified way that lens and vitreous opacities 

 are caused by eye-strain. The algebra has 

 suffered in one or two places from clerical 

 errors, and the table at the top of page 386 

 seems to have been obtained empirically under 

 conditions which, if well understood, have 

 certainly not been accurately described. 



The letter press is as good as could be de- 

 sired. The illustrations that have been made 

 for the book are excellent. Their number is 

 greatly increased by those borrowed from the 

 instrument-maker, whose courtesy serves a 

 double purpose. On the whole the author, 

 publisher and instrument-maker should be well 

 satisfied with the accomplishment. 



William S. Dennett. 



New York City. 



BCIENTIFIC JOURNALS AND ARTICLES. 

 The May number of the Botanical Gazette 

 contains the following papers : Ethel Sargant 

 has written concerning ' The Evolution of the 



