PROCEEDINGS OP THE SOCIETY. 
911 
Prof. Bell said they had another paper upon the Agenda for the 
evening, upon a new rotifer, Notops ruber , by Mr. J. Hood, but as that 
gentleman had since intimated that he had a further paper bearing upon 
the same subject, they had decided to take both at their next meeting. 
Mr. Hood had, however, sent up a number of living specimens of the 
new rotifer, which were being shown under the Microscopes on the table, 
and Mr. Rousselet would say something about them so as to direct 
attention to them whilst there was an opportunity of seeing them. 
Mr. C. Rousselet was sorry to say that they were nearly all dead, 
having unfortunately been too tightly corked up in a bottle without 
sufficient air. 
'Mr. E. M. Nelson said that as priority of invention occupied a 
place in the Proceedings of the Society it might interest the members to 
know that the reflecting paraboloid (generally called Wenham’s para- 
boloid) is figured as an illuminator for the Microscope in Goring and 
Pritchard’s ‘ Micrographia ’ (1837) p. 188, fig. 8, where it is stated to 
be the invention of the Rev. Mr. Packman. 
Mr. Nelson also referred at some length to the structure of the 
Microscope made by Messrs. Watson for Dr. Van Heurck, especially as 
regarded the fine-adjustment which was the subject of strong adverse 
criticism at the Society’s meeting of 20th May, 1891.* On that occasion 
the chief ground of objection taken was that the fine-adjustment being 
made on Zentmayer’s plan, which did not last, would be sure to fail in 
the same way, for the same reasons. Messrs. Watson had placed the 
instrument in his hands that he might independently test it, and he 
found that the fine-adjustment was not the same as Zentmayer’s because 
it was provided with spring stops which entirely obviated the evils 
complained of. A matter of some value which had been overlooked, 
was that the fine-adjustment screw was left-handed, by means of which 
the apparent and real motions were made to coincide, which was often 
a great advantage when working with high powers. He had worked 
with this Microscope for some time and had tested it in such a way as 
to enable him to speak of it with great confidence, and having found 
that the chief objection against it was one based upon a mistake, he felt 
sure it would be to the credit of the Society that the facts should bo 
stated, and that the adverse criticism should not stand. 
Mr. J. E. Ingpen said, with regard to the remarks made by Mr. Nelson 
as to the paraboloid illuminator, his own impression was that as it ap- 
peared in Goring and Pritchard it was only in the way of a suggestion, 
and that there was no reference to any stop for obtaining a black ground 
such as that employed by Mr. Wenham. He was speaking only from 
memory, but he thought he was right in saying that it seemed likely 
that^the idea as it appeared in Goring and Pritchard was never carried 
out practically. - 
Mr. Gill, having a lantern in the room at his disposal, took the 
opportunity of exhibiting an interesting series of photomicrographs of 
diatoms intended fc to demonstrate the nature of the markings by the 
* This Journal, 1891, pp. 399, 434, 558. 
