389 
Till . — The Royal Microscopical Society's Standard Screw-Thread 
for Nose-Piece and Object-Glasses of Microscopes. 
Being the Report of a Sub- Committee of the Council, drawn up by 
Conrad Beck, F.R.M.S., Secretary to the Sub-Committee. 
( Read lltli June , 1896.) 
The so-called Standard Screw-Thread of the Royal Microscopical 
Society has been but an imperfect standard, and has not ensured that 
interchangeability which it originally promised. It has been our 
duty to investigate the causes of this state of affairs, and to formulate 
a plan by which such an inconvenience should be remedied in the 
future. 
Without going too closely into the entire history of the subject, 
we propose to briefly explain the reasons why the original standard 
was not efficient for practical purposes, and then to state the plan 
which the Council of the Royal Microscopical Society has now adopted 
for the future. 
The specification of the original standard screw was as follows : — 
Form of Thread . — Whitworth thread, i.e. a Y-shaped thread, 
sides of thread inclined at an angle of 55° to each other, one-sixth of 
the Y depth of the thread being rounded off at the top of the thread, 
and one-sixth of the thread being rounded off at the bottom of the 
thread. 
Pitch of Screiv, 36 to the inch. 
Length of Thread on Object-Glass , 0*125 in. 
Plain Fitting above Thread of Object-Glass 0*15 in. long, to be 
about the size of the bottom of male thread. 
Length of Thread of Nose-Piece not less than 0 * 125 in. 
Diameter of the Object-Glass Screw at the bottom of the screw, 
0*7626 in. 
Diameter of the Nose-Piece Screw at the bottom of the thread, 
0*8 in. 
When the exact form of the Whitworth screw-thread is calculated 
it will be found that this allows a difference between the male and 
female screw of 0*0018 in., which is in itself quite sufficient margin 
of looseness to make an easy fit. 
The Society had two plug and ring gauges, one 0*8 in. and the 
other 0*7626 in., made by Whitworth as standards for the use of the 
Society, and it has been shown that if an adjustable tap and die (as 
recommended by the late Mr. Richard Beck in a paper printed in the 
‘Transactions of the Microscopical Society/ 1859, p. 92) be made 
which could be accurately adjusted to these standard sizes so that the 
tap exactly fitted the 0*8 in. ring size, and the die exactly fitted the 
1896 2 e 
