I40 THE MICROSCOPICAL NEWS. 
The application of the whole polarizing apparatus is very 
useful in working at the minute superficial structures made up of 
thin and highly refractive plates of organic carbonate of lime. 
The glare of light under ordinary illumination, and even when the 
polarizer only is used, prevents the true surface being focussed, or 
if it is fortunately hit upon, it is more or less invisible. But the 
analyser being placed across the direction of the polarizing ray the 
true surface can be found by the definition and distinctness of the 
clear colours and the intermediate lines. ‘Take away the analyser, 
and often new structures appear to the eye. As a matter of 
practice I find that this method is exceedingly useful. 
Circumstances have brought me in contact with cheap Micro- 
scopes, and certainly whilst it may be said that some of the 
objectives are fairly good, the eye-pieces are on the miserable 
“par” with the rest of the apparatus. I cannot avoid believing 
that during the next few years attention will be paid to increasing 
the merits and adaptability of eye-pieces whatever may be their 
special character. 
In the address which I had the honour of delivering to you last 
year I remarked upon the comparative values of object-glasses 
with high and low numerical apertures, and I took pains to defend 
the employment of lenses with wide apertures in examining 
minute objects, and also to state that both kinds of objectives are 
necessary for investigating into the structure of minute objects. I 
suggested what has commended itself to every advanced micros- 
copist for years past, that an observer should provide himself 
with both classes of objectives, and that he should use those with a 
moderate aperture for common and preparatory work, and those with 
a high numerical aperture for subsequent and careful examination. 
Very few microscopists care to correct their objectives during 
ordinary work, and principally because they have not seen the 
difference made in the appearance of an object by the process 
when it has been carefully carried out. But when an object, 
hitherto unsatisfactorily defined, presents itself under a clear and 
definite aspect, conversion to the opinion that there is an absolute 
necessity for correction in all delicate investigations regarding 
minute structures speedily ensues. ‘There is no doubt that with 
very few exceptions the microscopic work relating to the mor- 
phology of the animal and vegetable kingdom has been conducted 
either without corrected objectives, or with those which have an 
average adjustment. I pointed out in my last address how 
abnormally thick, slender and excessively minute bodies appear 
under a high amplification ; this is partly due to a want of correc- 
tion, and mainly to another cause which is not necessary to revert 
to. Now I have no hesitation in saying that similar abnormalities 
are constantly recorded as truths, and for that same reason which 
