REVIEWS 165 



field as something to be greatly desired in an objective. It is, however, now 

 universally recognised that these qualities are rather of a negative character, 

 and that they can only be secured by sacrificing other qualities that are of 

 greater importance. 



Difierent methods of illumination and appliances for obtaining these 

 results are described, and the illumination of objects by transmitted light, 

 as well as that ordinarily known as dark-field illumination, is well dealt with. 

 The method of using ultra-violet light, both for photographic purposes and 

 for observation of the fluorescent image produced thereby, is referred to, 

 but it cannot be said that the description is sufiiciently accurate, or complete 

 enough to enable anyone to attempt such work. Very few microscopes are 

 described, and then only so that the type may be appreciated. This is a 

 point that might well be followed in other books of this character, as it is 

 quite easy to refer to makers' catalogues to know what microscopes are being 

 produced ; one hardly needs a large portion of a book to be devoted to what 

 are, after all, but abstracts from these catalogues. 



Various types of ultra-microscopes are described in contradistinction to 

 the ordinary dark-ground illuminator. It is rather to be regretted that the 

 point of difference between resolution in the microscope and the visibility 

 that can be secured by any method of dark-ground illumination is not more 

 fully dealt with both in theory and practice. 



The chapter on useful microscope accessories and laboratory equipment is 

 of considerable interest, and should prove of service to those other than 

 chemists who have occasion to use the microscope. 



The chapter on Micrometry is equally useful. There follow sections on 

 Quantitative Analysis by Means of the Microscope, the Determining of Melting 

 and Subliming Points, the Determination of Refractive Index by Means of 

 the Microscope, the Examination of Crystals under the Microscope, and 

 methods for handling certain classes of material, and all of these are of 

 great interest. 



Chapters XIII, XIV, and XV refer particularly to the methods of micro- 

 chemical qualitative analysis, and reference to the book itself must be made 

 for this portion to be appreciated. 



In general the book may be regarded as a praiseworthy effort to deal with 

 the subject of its title, and may be commended to those engaged in micro- 

 chemical work. J. E. B. 



The Blicroscope. A Simple Handbook by Conrad Beck. [Pp. 144, with 

 131 figures.] (London : R. & J. Beck, 1921. Price 2S. 6d. net.) 



This book is intended as a guide to the use of the microscope. The correct 

 use of the instrument follows directly from a knowledge of the functions of 

 the difierent parts ; it has therefore been found best to develop the method 

 of manipulation in the course of the descriptions of its component parts. 

 Such particulars as are given of the optical principles and construction are 

 of the simplest character, and their comprehension requires no optical 

 knowledge. Certain theoretical matters are referred to in this book, but are 

 not explained . Some of the descriptions may appear to be extremely element- 

 ary to experienced microscopists, but even they may find useful matter 

 v/hich is not available in the ordinary textbooks. 



The earlier part of the book describes the various accessories that are 

 arailable and the method of their use ; the mechanical construction of the 

 stand being left to the last, a course of procedure that has much to recom- 

 mend it. 



The importance of illuminating apparatus is fully recognised, and methods 

 of use are described in such a way as to be intelligible to the novice. 



An early section is also devoted to the method of holding microscopic 



