274 ON SMITH AND BECK’S ACHROMATIC MICROSCOPES. 
great objects of which was to cultivate those scientific re- 
searches by which this ‘mere toy” of the Royal Society 
might be made available for the profound scientific researches 
for which it was adapted. One of the indirect results of the 
rejection of the Royal Society of Mr. Lister’s practical sug- 
gestions was his connection as friend and adviser of certain 
microscope-makers in London. From these houses have 
issued the most perfect microscopes that have been constructed 
in accordance with Mr. Lister’s principles. No one of these 
houses has been more distinguished than that of Smith, 
Beck, and Beck, and in Mr. Richard Beck, the author of the 
present volume, we have a remarkable instance of the combi- 
nation of the finished mechanician and accomplished observer. 
Previous, however, to Mr. Beck entering the field as an 
author, the late Mr. Andrew Ross, the founder of one of our 
great microscope-making houses, had written a valuable work 
on the physical principles involved in the manufacture and 
in the structure of the microscope. This work originally 
appeared as an article in the ‘ Penny Cyclopedia,’ and may 
claim priority over all the works that have been devoted to 
the history and structure of the microscope during the last 
quarter of a century. 
The present work is not intended to serve as a history of 
the manufacture of microscopes or of microscopic observa- 
tions of optical principles. But it gives an accurate account of 
the structure and capabilities of Smith and Beck’s instruments. 
It is hardly necessary that we should say that whatever the 
microscope demands for its intelligent and successful applica- 
tion is provided by this establishment, hence this work 
becomes a most useful text-book to all who are seeking for 
the best means of conducting microscopic researches. The 
work consists of a detailed account of the various parts of 
which a microscope is composed, and commences with a 
description of first- and second-class achromatic microscopes. 
All the apparatus for the working of such microscopes is 
described, and is followed by plain directions for the use of the 
microscope. These directions include remarks on the various 
k nds of illumination, and the apparatus which have been 
invented for assisting illumination. In the remarks made by 
Mr. Beck on illumination reference is made to the use of test- 
objects for measuring both the defining power of the object- 
glasses and the means of illumination employed. Whatever 
instruments are employed, these remarks will be found use- 
ful. A considerable space is devoted to the consideration of 
the subject of polarized light to the microscope, and all the 
apparatus required is described. Mr. Wenham’s binocular 
