330 Recent Microscopic Literature. 



without the draw-tube, and with a first eye-piece, or with a 

 lower objective of actually larger angle, with a deeper eye- 

 piece, or with a few inches of draw-tube. 



We have heard an experienced niicroscopist speak as Mr. 

 Brooke does in one of his conflicting remarks, that he could 

 see all with his ~th that he could see with his -^th ; but it 

 appears to us that this question wants carefully working out 

 with especial regard to penetrating power. When an object — ■ 

 other than diatom lines — has been seen with a |tli or -^th, can 

 it not nearly always be shown by ith ? A good -ith will work 

 well up 700 or 800 or 1 000 linear, and most things that can 

 be seen with .2000 linear can be made out with half that power 

 when their existence is known. 



We are abandoning excessive angles of aperture in this 

 country, and the Americans are resorting to them. This will 

 give rise to inquiry as to the value of their observations, 

 and when such observations necessarily require penetration, 

 accompanied by fine definition, we should be disposed to doubt 

 the correctness of the appearances brought out by objectives in 

 which the angle of aperture was very large in proportion to 

 focal length. 



So long as microscopic students are merely engaged in lay- 

 ing the foundation for original inquiry it may be doubted 

 whether they will do any good with a magnification of more 

 than 500 lineai*, but when original inquiry begins, high powers 

 become indispensable, and the best mode of obtaining them 

 is an important consideration, on which we should recommend 

 new and careful experiments to be made. 



Passing from points which experienced microscopists are 

 alone qualified to discuss, we come to subjects of more general 

 interest, and congratulate Mr. Davies on the aid he has afforded 

 to microscopic students by his compact work on preparing and 

 mounting microscopic objects. His book is necessarily and 

 avowedly in the main a compilation, but the reader has also 

 the advantage of the author's personal experience, and will 

 derive much information, not only with respect to different 

 methods of mounting, but likewise concerning the treatment 

 which particular objects require. The instruction ranges over 

 a wide iicld, comprehending diatoms, desmidsj sections of 

 organic and mineral substances, anatomical preparations, dis- 

 sections, etc., and the directions are given in a clear, agreeable 

 style. 



In mounting objects it is customary to use Canada- balsam 

 thinned with spirits of turpentine or camphinej but it is often 

 desirable t<> obtain the resinous matter in a more liquid and 



Volatile Solution. One good plan is tO dissolve thick balsam 



iii wood naphtha, or pyroiigncous ether, which is byfar the besi 



