471 



to remark that, in addition to the microscopical periodicals 

 mentioned, the library contains a fair number devoted to Natural 

 History pure and simple, such as the '' Annals and Magazine of 

 Natural History," "The Midland Naturalist/' "The Proceedings 

 of the Zoological Society," etc. Why these should be in "a 

 Patent Office library is not quite evident, but the microscopist 

 who is also interested in biological matters need not inquire too 

 closely into that question. D J S 



The Common Basis of the Theories of Microscopic Vision 



TREATED WITHOUT THE AID OF MATHEMATICAL FORMULAE. By 



Julius Pvheinberg, F.Pv.M.S. 9 x 6 in., 35 pages, 35 figures 

 in the text. Leipzig, 1902 : S. Hirzel. London: Williams 

 & Norgate. Price Is. Qd. 



A student of general optics, upon turning his attention to 

 microscopical problems, as treated by microscopists, is usually 

 struck by two facts. He cannot but be impressed, in the first 

 place, by the large number of important optical problems, 

 which are practically peculiar to the microscope, and of which 

 the cUscussion is practically confined to microscopists. Secondly, 

 a perusal of the literature of the subject leads to the conclusion 

 that many writers have specialised too soon. While treating, it 

 may be mth ability, the most recondite and difficult problems, 

 they are continually going astray and wasting their energies in 

 consequence of their imperfect knowledge and appreciation of the 

 fundamental principles of the science. For instance, in a paper 

 by a microscopist of deserved repute, it has been seriously con- 

 tended that a plane mirror brought converging (sic) skyfight to a 

 focus in the same way that a concave mirror brought parallel light 

 to a focus ! Much otherwise useful work has thus undoubtedly 

 been minimised in value. The latter consideration applies with 

 peculiar force to much that has been written and said on the 

 subject of microscopical vision. Ambitious work has been marred 

 by an imperfect comprehension of the sine-law ! Mr. Rheinber^^'s 

 brochure should therefore be received with pleasure and read with 

 profit by students of microscopical optics. It is not ambitious in 

 its aim— it does not profess to do more than present the simple 



