PROCEEDINGS OF THE SOCIETY. 
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were they needful for the highest class of even ordinary histological and 
general work, or not ; or were they the outcome of a want of knowledge 
as to what was essential? If the former, then the further question 
might be asked, was the Continental form of Microscope the best form 
in which they could exist ? At that late period of the evening it was 
not possible for him to go fully into the answer to this question, but 
he would just take up one point by way of illustration — the introduction 
of the condenser — and he carried with him the experience that without 
a good condenser good results could not be obtained 'from the best 
objectives. It had been found to be absolutely necessary that the con- 
denser should be accurately centered with the other optical arrangements. 
This being so, it was most important to see that the form of substage 
introduced on the Continent was bound by certain limitations of size 
and length of the hand, as they had been told, which entirely crippled 
its usefulness as a means of research, and they found that the German 
substage had no centering apparatus fitted to it because there was no 
room for it, and yet it was a peculiarity of the Microscope made by 
Zeiss ten years ago that a sort of substage arrangement was made to 
receive diaphragms , and this was provided with a centering arrangement ! 
The diaphragms were so minute that the makers could afford to make a 
light centering apparatus, and they did ; but the condenser was still 
utterly incapable of being centered ; that is to say, the delicate centre 
of an optical combination was allowed to take care of itself, but a 
diaphragm aperture was mechanically centered — yes ! and provided with 
rack and pinion besides — which was also wanting for the condenser. 
When Zeiss introduced their first (chromatic) condenser, it did not 
so much matter about centering it, but with the achromatic condenser the 
need was at once apparent. W hat can be the use of a delicately achroma- 
tized combination without an accurate use of its optical centre ? Hence 
we find that, unable to provide a proper centering socket in the substage 
of the Continental stand, because the space was so small, they provided 
their achromatic condenser with a separate and independent centering 
arrangement ; so that to get this condenser for the Continental stand we 
had to pay the additional cost of mechanical centering arrangements 
attached to it. But how does this work in practice ? It will be readily 
seen. The meeting will remember that Zeiss subsequently produced 
that remarkable objective which has a N.A. of 1*60. Now it was bound 
to have a condenser with an equal aperture ; to employ this then, it must 
of course have centering arrangements ; now I possessed their achromatic 
condenser and its special centering arrangements ; but these, not being 
in the substage, could only be of use when it was employed. The result 
was that to centre the new 1 • 60 N.A. condenser, it was needful to mount 
it also with a separate centering arrangement ! Thus there was the cost 
and inconvenience of a distinct arrangement for as many condensers, or 
other pieces of substage optical combination, as required centering. But 
in the English model the one centering substage received and centered 
every piece of substage apparatus ; this one expense covered all, and the 
collimation of the optical axis was more definitely and accurately 
secured. But in the Continental stand, from the very “ hand-breadth ” 
limits of its mode of genesis, this was impossible. It was too cramped 
to admit of a large centering substage. 
