158 Transactions of the Society. 



material assistance to the Council ; for it must be obvious to everyone 

 that apart from the co-operation of Microscope manufacturers, any 

 scheme of this kind must fall through. 



On investigation it was found that a Whitworth plug and ring 

 gauge of 1*527 in. for substages had been used by Messrs. Smith 

 and Beck many years ago, and that Mr. T. Ross had in 1863 adopted 

 this identical gauge, and that subsequently it had also been adopted by 

 Messrs. Powell and Lealand. As the majority of our English manu- 

 facturers had followed suit, the substage was already standardised by 

 the trade themselves, in this country at least, so your Council had 

 nothing further to do than to recommend that that gauge be adopted. 

 In this connection it was not necessary to consult with our confreres 

 either on the Continent or in America, because on the Continent a 

 substage, as we understand it, is practically unknown, a condenser- 

 fitting being used instead ; and in America nothing but Microscopes 

 on the Continental model are now manufactured. 



Now, with regard to the eye-pieces ; it was evident that the draw- 

 tube of the Microscope required standardisation, and not the tube of 

 the eye-piece itself, for the reasoa that ordinary eye-pieces ought to 

 fit loosely, so that they may be easily changed without any risk being 

 incurred of shifting the position of the body ; whereas for a screw 

 micrometer eye-piece the fit should be somewhat tight, to prevent it 

 rocking about in the draw-tube when its screw-head is revolved. Your 

 Council, therefore, wisely determined to standardise the inside gauge 

 of the draw-tubes, and not the outside gauge of the eye-piece tubes. 



With regard to the first or smallest size, there was no hesitation 

 in adopting the Continental gauge ; neither was there any difficulty 

 experienced in selecting the largest gauge, because that was limited 

 by the size of the field-lens of a 2-in. focus Huyghenian eye-piece 

 for use in a long tube Wenham binocular. 



With regard to the second size, it was found necessary to 

 standardise some such gauge as this, because many of our English 

 manufacturers make their smaller Microscopes, for medical students 

 and school purposes, about this size in preference to that of No. 1, 

 because a larger field can be obtained with the lowest power eye-piece, 

 and a large field is of much assistance when it is necessary to find 

 some particular object. 



The Council considered it necessary to standardise a fourth size, 

 intermediate between Nos. 2 and 4, suitable for medium-sized bino- 

 culars, for which purpose No. 2 is obviously too small, and No. 4 

 quite unsuitable, because a Microscope capable of carrying so large 

 an eye-piece as No. 4 must be of the largest size, and consequently 

 expensive. (It is quite remarkable what a notable difference a single 

 tenth of an inch in the diameter of an eye-piece makes in the total 

 size of a properly proportioned Microscope.) 



For gauges Nos. 'i and 3, a mean size of the various manufacturers' 

 gauges was in each case adopted, 



