PROCEEDINGS OF THE SOCIETY. 
311 
Dr. Edmunds thought that the whole question of microscopical 
measurements wanted going over and revising. It had been said that 
there was a Society’s screw for objectives, but when he wrote to the 
Assistant-Secretary to ask him for a standard gauge, he was told he 
could not be supplied, and so he found that his mounts of Powell and 
Lealand’s would not fit Eoss’s, and that Smith and Beck’s again 
differed from these. 
Mr. Beck said, there certainly was a standard in the possession of 
the Society, which was made by Whitworth at the time the question 
was settled, and there could be no doubt that by applying to 
Whitworth they could get others so exactly the same that all made to 
it must accurately fit one another. The differences now complained 
of were owing to makers not having revised their screw tools from 
time to time, so as to ensure that they were accurate. 
Dr. Edmunds said that there were also other questions that 
should be pronounced upon by the Council. For instance, what is 
the “ 10-inch ” tube? In practice the length varies with each of the 
makers, and the eye-pieces are so constructed as to destroy all 
uniformity in the datum point at the eye end of the tube. Practically 
the eye end of the tube measured from the diaphragm in the eye- 
piece. Nevertheless the 2-inch eye-piece — one of the chief makers 
only excepted — was shouldered about an inch beyond its diaphragm. 
On the other hand the ^-inch eyepiece necessarily has its shoulder 
about on a level with its diaphragm. It followed that in changing 
the 2-inch eye-piece for the J-inch the optical tube was lengthened 
no less than an inch. Therefore the amplification given by the 
objective at the point where it was taken up by the eye-piece, was 
greatly increased while the objective itself needed to be readjusted, 
and to have its focus shortened before it was fit to be viewed by the 
J-inch eye-piece. Yet all this could be remedied by the simple plan 
of shouldering the eye-pieces on a level with their diaphragms. Then 
again, why should not the visual and substage tubing of the large 
microscopes always be of the same size ? At present several of the 
chief firms made their substage tubing different in gauge from their 
own visual tubing, and consequently the eye-pieces could not be used 
for condensers. Nor was there any adequate reason why all the 
large microscopes, and on the other hand, all the small microscopes, 
should not be made to a standard gauge, so that apparatus made by 
various makers could be used indiscriminately. 
The President said that as to the standard of the Society’s screw, 
that was carefully kept in the possession of the Council, and copies 
could no doubt be obtained from Whitworth if they were required. 
With regard to the present discussion, it would be understood that 
Mr. Beck would be kind enough to give them his ideas on the subject 
of micrometric measurements, and that Dr. Edmunds would similarly 
undertake the other questions as to size of screw, tube, &c. 
A letter was read from Mr. F. Habirshaw, of New York, in reply 
to one addressed to him by Mr. Crisp in reference to the discussion 
that had recently taken place on the “ Kevification of Diatoms,” and 
particularly the note on p. 150, in which Mr. Habirshaw said. 
