224 
NOTICES OF NEW BOOKS . 
Critical Microscopy. How to get the best out of a microscope. 
By Alfred 0. Coles, M.D., D.Sc., etc. 1921. viii + 100 pp., 
8 illustrations. Published by J. and A. Churchill, 7 Great 
Marlborough Street, London. Price 7s. Gd. net. 
The author states that this small book may be regarded as a 
supplement to, rather than a substitute for, the many excellent works 
on the microscope now available ; and it is written with the hope of 
assisting microscopists, whatever may be their special line of work, to 
get the very most out of their instrument. 
The term “Critical Microscopy ” is due to Mr. E. M. Nelson, and 
full credit is given to him for the methods described ; the book in fact 
consists, in large part, of extracts from writings or from direct commu- 
nications from Mr. Nelson. It opens with a description of an ordinary 
microscope, but no attempt is made to describe a number of types. 
The only one figured is the Service Microscope, made by Messrs. W. 
Watson and Sons, and as this does in fact represent a microscope made 
in this country for student’s purposes at the present time, it may be 
regarded as typical. It is the design of stand recommended by the 
British Science Guild Committee on Microscopes, and has the particular 
advantage that it can at any time have added to it any additional 
appliance that may be needed for more advanced work. 
The various types of objective are described, and the writer indicates 
those that are suitable for particular classes of work, rightly indicating 
that a large variety of objectives is by no means necessary. He further 
states that the use of apochromatic objectives is not essential for work 
even of the highest class, a point that every practised microscopist 
realizes. It is by no means now common to see a high-power 
apochromatic objective being used with an Abbe non-achromatized 
condenser of an ordinary type, the result being that the advantage of 
the apochromat is largely lost. 
A suitable series of oculars is indicated, and preference is given to 
those of the compensating type, even in cases where achromatic 
objectives are used. The author also prefers a triple nose-piece rather 
than the sliding objective-changers as introduced by Zeiss. When the 
triple nose-piece is well enough made to ensure accurate centration and 
perfect alignment of optic axes no doubt it is satisfactory, but for 
some classes of accurate work it is probable that the sliding changers 
are to be preferred. 
As an illuminant the paraffin lamp is recommended. A bull’s-eye 
condenser is used in conjunction with this, and is fitted to the lamp as 
an integral portion of it, so that any alteration in the position of the lamp 
does not disturb the relation of the illuminant to the bull’s-eye condenser. 
The author’s arrangement of lamp, screen-holder, eye-shade and 
microscope is figured, and is so arranged that the whole outfit is fixed to 
a board, ensuring the proper and constant relation of the various items. 
