September 12, 1913] 



SCIENCE 



367 



■who later find their way to college or univer- 

 sity. No better groundwork could be found 

 for college or technical school physics than 

 the ability, on the part of the student, to apply 

 the science to his every-day problems. 



The volume is one of the series which ap- 

 pears under the title " The Teachers Profes- 

 sional Library," edited by Nicholas Murray 

 Butler. The Macmillan Company is to be 

 commended for the attractive and substantial 

 form which the book has been given. 



F. E. Kester 



Thich Lens Optics. An elementary treatise 

 for the student and the amateur. By 

 Arthue Latham Baker, Ph.D., Manual 

 Training High School, Brooklyn. N". Y. 

 D. Van Nostraud Co. 1912. Pp. ix + 131. 

 $1.50 net. 



University texts on optics, as a rule, treat 

 first order lens theory but incompletely and 

 the aberrations of the third and higher order 

 scarcely at all. The average university in- 

 structor in physics regards geometrical optics 

 as an alien subject properly disposed of in 

 high school. Reference texts of lens theory, 

 on the other hand, deal largely with the third 

 order theory and fail to give an elementary 

 comprehensive treatment of first order theory. 

 Baker's little lens primer well fills this gap 

 between the university text and the special 

 treatise and will be heartily welcomed by 

 oculists and by manufacturers and users of 

 spectacles and other low-power lenses. It is 

 confined strictly to first order theory, giving 

 a simple and able treatment of image forma- 

 tion and focal power of combinations of thin 

 and thick lenses. Diagrams are plentiful and 

 good. A great many numerical examples are 

 given and one chapter is devoted to the ex- 

 perimental determination of the optical con- 

 stants of lens combinations with simple appa- 

 ratus. When the book is revised it would be 

 well to adopt a less formal style and perhaps 

 either add a chapter on the special problems 

 of spectacle lenses or mould the whole into 

 an introduction to advanced lens theory. 



P. G. Nutting 



Prisms. Their Use and Equivalenis. By 

 James Thorington, A.M., M.D., Ophthalmic 

 Surgeon, Professor of Diseases of the Eye 

 in the Philadelphia Polyclinic. P. Blakis- 

 ton's Son & Co. 1913. Pp. 144. 

 This little book is based on its author's 

 course of lectures on this subject delivered 

 each winter at the Philadelphia Polyclinic. 

 It deals with the use of prismatic spectacle 

 glasses in correcting muscular defects of the 

 eye. Methods of evaluating prisms combined 

 with spherical and cylindrical lenses are de- 

 scribed and a number of useful tables given. 

 The diagnosis and measurement of imperfect 

 muscular balance (heterophoria) and of devia- 

 tion from parallelism (heterotropia) of the 

 eyes are discussed at some length. The book 

 is well written and well illustrated and bears 

 evidence on every page of the author's grasp 

 and first-hand knowledge of the subject. 



P. G. NUTTIKG 



SPECIAL ARTICLES 

 a parasite of the chinch bug egg 

 In the experiments conducted this year to 

 determine the time of the first appearance of 

 young chinch bugs and the mortality of the 

 eggs, a large number of eggs were collected in 

 the field for examination. The eggs which 

 were collected at different intervals and in 

 different localities were examined daily. 

 While thus examining the eggs it was noticed 

 that some of them became dark in color instead 

 of assuming the usual red coloring. These 

 eggs were isolated and on May 19 there 

 emerged from them three parasites. With 

 these three parasites as a basis, the life history 

 was carried through four generations, running 

 up to July 5. Since this was the time between 

 the two broods of the chinch bugs, it became 

 impossible to obtain additional chinch bug 

 eggs with which to continue the work. From 

 July 5 to July 23 only an occasional para- 

 sitized egg was found in the field, but 

 beginning with the latter date, parasitized 

 eggs were found in large numbers in the 

 corn fields and the second generation was ob- 

 tained by August 10. IJp to the present date 



