282 
PROCEEDINGS OF THE SOCIETY. 
species had been described as new ; the literature of these things was so 
wide-spread that it was hardly possible to know at first whether a thing 
was new or not, but it was a very good thing to have any misapprehen- 
sion of this kind corrected as soon as possible, and before it got into 
print, so as to prevent the inevitable confusion which would be sure to 
otherwise arise. Their thanks were due to those gentlemen who had 
sent them these communications, and he moved that a special vote of 
thanks be sent to those who had sent the specimens of deep-sea soundings 
and diatomaceous earth. 
This was unanimously agreed to by the meeting. 
Mr. Nelson read a paper “ On the Chromatic Curves of Microscope 
Objectives ” (ante, pp. 5-17). 
Dr. Dallinger said that it would be neither necessary nor wise at that 
hour of the evening to have much to say upon the very interesting 
subject before them. The paper was one which was self-contained, and 
its real value would only become fully apparent when they saw it in 
print and could read and study it for themselves. Since the use of 
monochromatic light had been employed by them for microscopical 
purposes, he had used it in various forms, producing it by different means, 
both by daylight and lamplight, and nothing could be more remarkable 
than the results which he had obtained with a series of lenses which had 
been produced for him by the best English and foreign makers, extending 
over a period of twenty-eight years, every one of which he still retained 
in his possession. Many of the results so obtained were as notable as 
they were curious, so much so that they would require some study on 
the part of experts to explain them, and the explanation in detail 
certainly would be most valuable from a practical point of view. 
Mr. Nelson had been quite right in pointing out that unless we could 
devise means for employing the shorter wave-lengths of the spectrum, 
we had approached very near to the limits of visual possibility with the 
means at present at our disposal. He had not been able in the time at 
his disposal to go into the details of the explanation of this statement, 
but they might accept it as a fact, and he thought that what Mr. Nelson 
had to say in his paper on this subject would clearly demonstrate that 
it was so. But as to the belief expressed by Mr. Nelson, that glass such 
as was used in our object-glasses was not transparent to the higher 
violet and the ultra-violet rays, and to some extent also to the blue, it 
must be remarked that there could be no doubt but that the figures of 
the lenses had much to do with this. It led them up to the consideration 
of the question as to what would be a suitable form and medium for 
lenses capable of allowing the higher rays to be used. There could be 
little doubt that all who believed in a future advantage in the use of 
monochromatic light, also foresaw that there must be lenses specially 
prepared for its use — wholly adapted, indeed, to the purpose. They all 
knew now that they had reached the limit of possibility so far as present 
materials were concerned, for if a lens could be made with a N.A. 
of 2 • 00, there was no liquid medium to use with it, but even if they 
could carry their lenses further they could not mount objects in any 
media which would give them a further advantage, because no medium 
