MICROSCOPY. 567 
their mathematical argument upon the improved assumption that 
the conditions under which the law of reduced apertures operated 
were, and must necessarily be, the same in all objectives as in 
those which were in their hands. This fallacy in the mathematical 
argument has been already pointed out in this Journal, as well as 
by Dr. J. J. Woodward in the + Monthly Microscopical Journal.” 
Now that the doctrine of the limitation of the balsam angle of 
objectives, plausible and strong in seeming to rest upon well 
nown facts, is removed from the way of progress in the science 
it was designed to assist, it remains to discuss the -means of ac- 
complishing an increase of this angle, and whether such increase 
may add to the working qualities of the objectives possessing it. 
Mr. Tolles, who must be admitted to have been the first to claim 
such increase of angle, believes it to be a valuable addition to 
the powers of objectives. The following letter from him contains 
some further discussion of the means of increasing the balsam 
angle, as well as some claims in regard to his personal relation to 
the controversy. 
Dr. R. H. Warp, Sir :—I have read your notice, in the July 
Number of the Naruratist, of a current discussion as to possible 
balsam angular aperture of objectives. I am gratified at its evi- 
dent spirit of fairness; and will ask that, in the same temper, you 
will give place to some strictures of my own. 
The ;4; measured in London had, and has, no point of adjust- 
ment where with appropriate cover thickness the definition would 
hot be good. Its highest angle, when immersed in water, is about 
midway of the total adjustment, and at this point corrects for y's 
inch cover. All this I will show you any time; also, Dr. J. J. 
Woodward has verified the same. 
There is no secret as to the mode of action and the plan. The 
theory has been openly declared in every article of mine having 
the form of reply to Mr. Wenham since his first denial of validity 
of my first ‘‘experiment.” Thus, while admitting and declaring 
the reduction of refraction at the first plane surface, by immersion 
in a more refractive medium than air, every suggestion on my part 
has been of some way of making up for that loss. You say I 
appeal to facts not discussing principles. What induced my first 
experiment was a clear apprehension of law, and the result was 
confidently asserted beforehand. I have never denied that the air 
