ADDRESS TO THE ROYAL MICROSCOPICAL SOCIETY. 139 
full as it is, were crowded by those scientific men who constantly 
use the Microscope in original research in biology. A considerable 
experience impresses me that the majority of ‘students, and not a 
few professors, not only use indifferent instruments, but also care- 
fully avoid all those practices which we know are absolutely 
necessary for correct microscopy. <A thing is seen, therefore it 
must be real ; one man sees a spiral line, another a circle, another 
a series of dots, using the same object and different Microscopes. 
They describe, and debate, and each is self-satisfied. Yet all the 
while had they had a master in microscopy their differences could 
be terminated. 
A pleasant evening with the Microscope generally means a 
painful time for the eye. A good glare of light, thanks to lamp, 
condenser, mirror, and forgotten diaphragm, appears to be almost 
invariably a desideratum to the beginner. Experience teaches, 
however, and the advanced microscopist never uses more light 
than is absolutely necessary, and increases and diminishes the 
illumination during the careful observation of an object, not only 
by employing a less intense source of light, but also by using 
diaphragms of different sizes. 
Since microscopy has been extended to the examination of 
sections of rocks composed of different minerals, the truth that 
some can be roughly distinguished by their dichroism under the 
polarizing ray, the analyser not being used, has become apparent. 
The polarizer is also useful in another manner. Researches have 
been undertaken to examine into the influence of the polarizing 
ray upon substances which may or may not give the usual 
phenomena under the analyser. Polarized light carefully manipu- 
lated is very useful in examining thin sections of corals which 
are made up of closely placed fusiform and long alternating 
prisms, with geometrical prisms of carbonate of lime in planes one 
over the other, and often radiating from different points. Shadow 
and high light succeed when the Nicol is rotated, and minute 
details become apparent which are not seen, or are only feebly 
defined, by ordinary light reduced in its intensity to that of the 
polarizing ray by the use of diaphragms. 
Some time since, in investigating the structure of a fossil which 
was composed of close radiating and occasionally inosculating 
tubes with very thin walls and a distinct lumen, all mineralized 
with calcite in the glassy, non-crystalline form commonly seen in 
fossils where there is much space unoccupied by structure, the 
polarizing ray certainly made the tubes more distinct than the ray 
reflected from the mirror alone, and by rotating the substage 
Nicol, the position of certain tubes which were invisible before 
could be ascertained ; that is to say, dark lines appeared limiting 
tubes which were invisible under ordinary illumination. 
