ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
227 
(5) Microscopical Optics and Manipulation. 
A Treatise on Photographic Optics, by E. S. Cole.* — The contents 
of this book are well described by its name ; for its scope embraces a 
discussion of the optical principles and optical difficulties of photo- 
graphy. In one sense it is not a practical manual, for it only incidentally 
notices applications of the art, and does not even make a reference to 
photomicrography. It avoids the ground of the ordinary handbook 
to photography, and does not trouble itself with the composition of 
solutions, the make of stands, or with manipulative details at all. But 
within its limits it is very practical, and is written with a clearness and 
a mastery of the subject that must place it high on the list of works of 
a similar nature. All points of theoretical interest connected with light 
and lenses are thoroughly explained, and are then elucidated by a con- 
clusive experiment performed usually with quite ordinary apparatus. 
The mathematical treatment is simplified as much as possible, but not so 
much so as to be unintelligible, and is invariably followed by a well- 
chosen numerical example fully worked out, so that no reader need be 
in perplexity about the meaning of a formula. But while no mathematics 
are used beyond the simplest trigonometry, the principles underlying 
those parts of the subject requiring more elaborate mathematical analysis 
are clearly stated, and the experimental illustrations remove all un- 
certainty. In this way such difficulties as “ least circle of aberration,’ 
astigmatism,” are freed from their usual obscurity. The illustrations are 
very numerous and well drawn, and the type is excellent. In his pre- 
face the author states that he has tried to avoid producing a book which 
should be useful only to the professed mathematician and physicist, but 
the mode of treatment will commend it to all interested in optics. A 
possible improvement in a second edition would be an appendix on 
optical bibliography. The contents of the book are in seven chapters : — 
i. On Light (pp. 3-38). ii. Elementary Theory of Lenses (pp. 39-121). 
Thin and thick lenses are very fully discussed on the Gauss method ; 
magnification ; combinations ; Dallmeyer’s telephotographic lens ; per- 
spective; swing-back. iii. Aberration (pp. 122-39). Spherical, including 
astigmatism ; chromatic, iv. Correction of Aberration and Design of 
Lenses (pp. 190-204). v. Lens Testing (pp. 205-50). Tourniquet 
System ; Kew system, vi. Exposure, Stops, and Shutters (pp. 251-93). 
vii. Enlargement, deduction, Depth of Focus, and Halation. 
(6) Miscellaneous. 
Takes’ Cover-glass Clip for making Blood-films. — This consists of 
a block of mahogany, B, fig. 59, with a strip of cork let in flush with its 
upper surface. The brass spring plate A grips the cover-glasses C upon 
the cork, and holds them fast. 
The advantages of this cover-glass clip over the forceps usually 
employed are : — that more than one cover-glass can be streaked with 
blood at a time ; that it is possible to obtain a single layer of blood-discs ; 
and that the cover-glass is not so liable to get broken. 
The clip was devised by Mr. W. C. 0. Pakes, of Guy’s Hospital 
* London, Sampson Low, Marston and Co., 330 pp., many illustrations. 
