NEW BOOKS, WITH SHORT NOTICES. 145 
objects. For the surprising diversity—not to say antagonism—of 
view entertained by different observers who have over and over again 
examined the same object and yet have interpreted so differently the 
appearances observed, could not but lead to the conclusion that the 
microscopic image itself is not always the same unaltered transcript 
of the same light and shadow picture. The more difficult therefore 
the problem placed before the microscope for solution, the more 
needful should it seem that the theory of the compound microscope 
.be again strictly revised, if the difficulties of interpretation which 
increase with every fresh strain put upon the instrument are to be 
overcome. By Teutonic minds the relegation of so congenial a labour 
into the hands of the optician was not likely to be tolerated ! and as 
little would they be content that such knowledge should lie outside 
the recognized sphere of scientific investigation. 
The physico-mathematical investigation of the theory of the micro- 
scope has thus naturally fallen into the hands of those for whom this 
subject possessed special attraction. But it may also be fairly expected 
that all who are interested in microscopic research generally, should 
desire to hear of any new discovery that might come to light, or of 
any fresh aspect in which what was already known might appear after 
renewed examination. A second edition of a well-accredited work has 
therefore real significance, and appears opportunely for the lovers of 
microscopic science at a period when the limit of the powers of the 
microscope seems to have been reached, and, in default of adequate 
explanation and rational guidance, a certain misdirection of energy in 
any further efforts to add to its powers becomes imminent. 
The work of Professors Nigeli and Schwendener, of which we 
here propose to give a short account, brings down to the end of the 
year 1875 the latest summary of the optical questions connected with 
the theory of the microscope and of the conditions under which the 
various objects submitted to microscopic analysis are seen. <A glance 
at the table of contents will best show the German method of handling 
a rather complicated theme, and the space occupied by each section 
will roughly indicate the relative importance of each. 
Section 1.—103 pages are devoted to the theory of the microscope 
and the demonstration of optical problems therewith connected. 
Section 2.—6 pages containing remarks and recommendations 
relating to mechanical arrangements, with 15 pages of description 
and woodcut illustration of foreign stands of various makers. 
_ Section 3.—60 pages occupied with discussion of modes of pro- 
cedure for testing the accuracy of optical construction and the relative 
values of lens combinations. 
Section 4.—50 pages. The theory of microscopic vision, including 
the phenomena of “interference”; the effect of illumination upon 
various objects seen by transmitted light direct and oblique; and the 
effects produced by objects in motion, and by changes of level (in 
focussing different planes). 
Section 5.—15 pages on the simple micr sroscope. 
Section 6.—35 pages on technical manipulation. 
Section 7,—62 pages on phenomena of polarization. 
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