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XXIX. Notices respecting New Boohs. 



Theorie der Optisclien Instrumente nach Abbe. Von Dr. Siegfried 



Czapski. Sonderdruck aits dem Handbuch der PJiysiJc von A. 



Winkelrnann, Band II. 1893. Breslau, Ed. Trewendt ; Williams 



and Xorgate. 

 HTHE subject of Geometrical Optics might with advantage be de- 

 ■*• fined so as to include all those parts of the theory of light and 

 optical instruments which can be treated by geometrical and formal 

 considerations, without detailed discussion of dynamical questions. 

 In strictness, of course, the Theory of Lighi; is a branch of Dynamics ; 

 but it is rather striking how completely the subject divides itself 

 into two distinct regions. The practically important part involves 

 but very slight recourse to dynamical treatment, while the specu- 

 lative part is almost wholly concerned with dynamical questions. 

 The title of Geometrical Optics to separate existence rests on 

 this fact : but it may fairly be urged that, in opposition to the 

 usual practice, the greater part of the subject of Diffraction and 

 Interference of light should be assigned to this branch of the 

 theory, on account both of its geometrical character aud of its 

 importance for the working of optical instruments. 



As ordinarily developed, the subject is a branch of Geometry 

 which is concerned with the refexion and refraction of rays of light. 

 But if it is severed too much from the practical applications that 

 gave it birth, there is perhaps no department of mathematics 

 that can be made so repulsive. In matters of Pure Mathematics 

 the natural mode of progress is to adhere closely to the track of 

 symmetry and elegance ; and there is no other canon of merit that 

 is applicable. But in the subjects that are cultivated more directly 

 for the sake of useful applications there is no choice of topics 

 allowed; and the aim must be to develop methods of investigation 

 that will satisfy the demand for mathematical elegance, and will 

 at the same time allow of an exact correlation between the mental 

 process and the natural phenomenon. 



The book before us is a treatise on Geometrical Optics, compiled 

 from the point of view of the Theory of Optical Instruments. The 

 position which Dr. Czapski holds, in conjunction with Professor 

 Abbe, in re^tion to the famous manufacturing firm of Zeiss at 

 Jena, is a guarantee th^t the more technical information contained 

 in the work is exact and up to date. From the aspect of theoiy, 

 perhaps the most valuable feature of the book is the very copious 

 reference to the works of original writers; for to obtain a real 

 command of any department of a subject of w r ide practical ramifi- 

 cations, the consultation of text-books, how T ever good, is but a poor 

 substitute for the assimilation of the ideas and points of view of 

 its original promoters. The treatise contains a very full account of 

 the topics which have been indicated above, with the exception of 

 the theory of Diffraction, of which the treatment is. presumably left 



