138 
TOPULAR SCIENCE REVIEW. 
MICROSCOPIC TEST OBJECTS UNDER PARALLEL 
LIGHT AND CORRECTED POWERS. 
BY THE REV. J. B. READE, F.R.S., P.R.M.S. 
HE characters of objects we can neither see nor touch can be 
revealed by the microscope only. We must have a magni- 
fying apparatus and an illuminating apparatus. The former, 
the magnifying apparatus, i.e. the whole battery of powers from 
£th to sVh of an inch, may be readily obtained from Messrs. 
Ross, Wray, Beck, and Powell ; and these eminent English op- 
ticians have spared neither labour nor expense in working up 
to the most elaborate formulae. The latter, the illuminating 
apparatus, has much wider scope — is untrammelled by definite 
rules of construction, and brought out under every variety of 
shape. A “ condenser ” is what we want, i.e. an instrument for 
giving a proper angle to a suitable pencil of light. But what 
a list we have to choose from ! Wollaston, Brewster, Shadbolt, 
Wenbam, Nobert, Amici, Gillett, Kingsley, Dujardin, Reade, 
cum multi8 aliis, are in the field, each one offering some pecu- 
liarity of construction or some special principle of illumination. 
Hence the optician himself is nonplussed here, and he can only 
say to his customer, in the language of the showman, “ Pay 
your money, and take your choice.” 
In attempting to make the microscope perfect as an instrument 
of research a universal testimony is borne to the importance of 
illumination ; and it is not too much to say that illumination is 
the soul of the complex body , with all its ingenious mechanism, 
appliances, and powers. In dealing with the problem of illu- 
mination a few years ago, I felt convinced that in all our 
condensers a most important desideratum was wanting. We 
had fixed apertures for all the powers and for all, even the 
[PLATE LVIIL] 
INTRODUCTION, 
TIIE “KETTLEDRUM.” 
