Monthly Mi ical 
RE Neer ae PROCEEDINGS OF SOCIETIES. 291 
and he was inclined to think that in histology, for the purpose of 
analyzing organic structures, the existing microscopes were, as the 
Yankees would say, “played out.” We have got as far as they will 
take us. He believed that a 3,th did not enable anybody to see any- 
thing which could not be seen with a good ;4,th of Ross. He consi- 
dered these deep objectives to be eminently delusive, and they were so 
doubtless for the reasons which had been stated by Dr. Pigott. He 
could not doubt that Dr. Pigott had got on the right track of showing 
what was to be done in the present state of affairs. Practically the 
nature of the question just now is whether, in an organic tissue, 
one could truly define a point not more than 5,1,,th of an inch 
in diameter. There was always that unhappy luminosity about the 
margins of such objects, which he did not doubt arose from the 
causes which Dr. Pigott had pointed out. Histologists, he feared, 
were at the end of their work unless, by the aid of some such appliance 
as Dr. Pigott had endeavoured to furnish, they could obtain micro- 
scopes which would enable them to separate two points the 100,000th 
of an inch apart. Only then could they say whether the object was 
homogeneous or not. At present when they talked about homogeneous 
solids or fluids, or attempted to define an object like Bacterium, they 
were absolutely in cloudland. He had come to the meeting in the 
hope that he might hear that some light had been thrown upon this 
subject ; and he did indeed trust that Dr. Pigott had proceeded some 
way on the road towards the solution of the difficulty ; at any rate, he 
had macadamized the road, and that was a great matter. 
Dr. Pigott, thanking Professor Huxley for the manner in which 
he had spoken of him, said he could well understand that so ardent 
a worker should feel the urgency of those wants to which he had 
referred. He thought, however, he might be allowed to say that in 
correcting the aberration of objectives, if there was nothing else to 
point to than a power of varying chromatic effects by means of the 
aplanatic searcher, a great improvement would have been made. The 
object-glasses of the present year were greatly in advance of those of 
previous years as regards the correction of visible error which must 
therefore have existed, however unsuspected and denied, for the very 
fact of their present superiority is a conclusive answer to the question 
as to whether any improvement had been made. 
Mr. Slack asked Dr. Pigott to throw some light upon the subject 
of the colours which he described as preceding and accompanying the 
resolution of beaded objects.* 
Dr. Pigott said: If a diatom slide as the Formosum were held 
obliquely, so as to let the sun shine upon it, then as the inclination of 
the slide was varied, the hues went through all the colours of the 
rainbow in regular and then in reversed order, thus exactly imitating 
the phenomena of the spherical falling drops of the rainbow, and 
proving the spherical nature of the beadings. He wished to make an 
announcement of the extraordinary power of varying the secondary 
spectrum shown by oil of cassia used instead of water, with the immer- 
* Dr. Pigott had exhibited a diagram in which the singular isolated disks of 
the Formosum had been seen in sunlight. 
