ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 537 



The Society's Standard Thread.* — E, M. Nelson makes the follow- 

 ing communication : — 



"Mr. Watson Baker, in the Journal of the Royal Microscopical 

 Society, 1911, p. 175, has called attention to 'the great diversity which 

 exists in the objective screw-threads made by the various makers, and 

 described as of the Royal Microscopical Society's standard size.' Possibly 

 a few remarks from one of the members of the sub-committee ap- 

 pointed by the Council of the Royal Microscopical Society to report upon 

 this very question may not be out of place, the more so as Mr. Watson 

 Baker's paper deals only with the facts which, apart from the history of 

 the subject, may cause very erroneous ideas to be formed. 



The Society's Screw. — Fifty-four years ago this screw was adopted by 

 the Microscopical Society of London, upon a report from a sub-committee 

 composed of George Jackson, Charles Brooke, and H. Perigal, jun. The 

 multiplicity of adapters had even then become such a nuisance that the 

 Society standardized a screw with a view to stopping it, and the thanks 

 of everyone using a Microscope is due to them for so doing. This 

 standard screw was at once adopted by the three leading London Micro- 

 scope makers — viz. Messrs. Powell, Ross, and Smith and Beck. (The 

 size of the screw was that used by Messrs. Smith and Beck, Mr. Smith 

 having brought it with him from Messrs. Tulley, of Islington ; he had 

 previously used it in making the celebrated Lister-Tulley Microscope. 

 The Tulleys had taken this screw from the "Pipe" of Benjamin 

 Martin's Microscope! (1760-70). When it was standardized it was 

 altered to a Whitworth thread ; but, notwithstanding, a Benjamin 

 Martin's " pipe," or a Tulley-Lister objective, will screw readily into any 

 R.M.S. standard nose-piece ; but an objective with a standard thread 

 is the merest trifle too large to enter either a Benjamin Martin or Tulley 

 nose-piece). 



Six months after the adoption of the report Mr. Richard Beck pub- 

 lished an account, with six figures, of the screw-gauges and tools. Two 

 plug and ring-gauges for the tops of the threads of the inside and outside 

 screws, and pairs of sizing-tools, were made by Whitworth, the sizing- 

 tools being supplied to the trade at cost price. At first there was, it 

 seems, a little grumbling and fault-finding, as was inevitable upon a 

 reform of this kind ; but soon things shook down and settled them- 

 selves, with the result that, in my own experience, I have never seen an 

 objective by Powell, Ross, or Beck, that was not interchangeable in 

 either of their nose-pieces, and I very much doubt if anyone else has. 



In the eighties, German object-glasses, by Messrs. Zeiss, Leitz, and 

 others, were largely imported, and at the end of that decade there 

 was a demand for sizing-gauges. One of the secretaries of the Royal 

 Microscopical Society, not finding any in stock, took an old tap he 

 happened to see in a drawer, and, without comparing it with the 

 standard gauges, and at a considerable expense, had it precisely re- 

 produced, and distributed the facsimile copies on the Continent. All 

 this was clone quietly, and no one knew anything about it. 



Some objectives I had purchased from Messrs. Zeiss had been sized 



* English Mechanic, xciii. (1911) p. 290. 

 t See this Journal, 1898, p. 474, fig. 81. 



