PREFACE TO THIS EDITION. 
OlNCE the issue of the last edition no radical 
^ changes, so far as 1 am aware, have been made in 
the optical part of my subject. There has, however, 
been a steady improvement in the cheaper lenses, a 
nearer approach to the apochromatics which still retain 
their position of pre-eminence. I have given a certain 
amount of attention to some of these new series of 
Object-glasses, Condensers, and Oculars. 
In the photographic department several very impor¬ 
tant advances have been made since last I treated of 
this subject. The orthochromatism of plates has been 
brought to a point of much greater excellence, culmin¬ 
ating in the “ Spectrum ” plates of Cadett. The 
printing processes at command are now more numerous, 
simpler, and in some cases better adapted to our 
purpose than former processes. These are carefully 
dealt with in the present issue. 
A new and greatly improved apparatus for very 
rapid photo-micrography, as well as a simple but very 
efficient one for very low power work on large 
plates, will be found described in this new edition. 
It is hoped that as the apparatus and processes at 
command become simpler and more efficient, the use 
of this branch of practical science will become more 
and more general. 
ANDREW PRINGLE. 
Basing House, Banstead. 
October, 1902. 
