222 PROCEEDINGS OF THE SOCIETY. 



It was also stated by Professor Eogers that lie had a large collec- 

 tion of micrometers by diflferent makers at home and abroad, including 

 transfers from every well-known j)rccision-screw in the United States ; 

 and although his investigations were not yet quite completed, he felt 

 safe in saying that no two of them agree at a given temperature, the 

 errors of subdivision being in many cases very large, and in all cases 

 easily measurable. 



Mr. Crisp further said that it was now four months since he brought 

 before the Society the resolutions passed at the Indianapolis Congress 

 of American Microscopists in August last, recommending the universal 

 adoption of the yi^ of a millimetre as the unit of micrometry. As 

 apart from the discussion that took place at the October and December 

 meetings,* the subject had been thoroughly ventilated in the interim, 

 there seemed no reason for postponing the subject further, and there- 

 fore with the view of bringing the matter to an issue one way or the 

 other, he would give notice of moving the following resolution at the 

 April meeting : — 



" That in the opinion of this Society the most convenient unit for 

 micrometric measurements would be the ^rno ^^ ^ millimetre." 



He had purposely abstained from framing the resolution as in 

 any way a recommendation which it might be considered they had no 

 right to make, leaving it to express simply the opinion of the Society 

 as to the most convenient unit. 



In supj)ort of the first point embraced by the resolution, viz. the 

 selection of a subdivision of the metre and not of the inch, it was 

 hardly necessary to remind the meeting of the extent to which the 

 millimetre was used at the present time in the scientific world ; whilst 

 as to the second point, the adoption of the yoVo ^^ ^ millimetre instead 

 of the j}fQ, it would be borne in mind that the former, which was first 

 suggested in Holland, was now the accepted Continental standard 

 (under the name of micro-millimetre), with the special symbol fx (or 

 sometimes Mik.), and was to be found in the works of both French 

 and German writers (particularly diatomists), and in the Proceedings 

 of the j)rincipal Continental learned Societies. Even without this to 

 recommend it, he thought there could be little or no difierence of 

 oj^inion that yIo of a millimetre was far too large a standard. 



If it was considered desirable for any purpose not to lose sight of 

 the inch altogether, the plan suggested by Mr. Beck of showing, on 

 one micrometer, subdivisions both of an inch and of a millimetre, was 

 a very convenient one. 



Professor Keith's paper, " Note on Mr. Wenham's paper ' On the 

 Measurement of the Angle of Aperture of Objectives,' " was taken as 

 read in consequence of the lateness of the hour. 



Mr. ToUes' paper on " An Illuminating Traverse Lens " was post- 

 poned until the next meeting. 



* See tliia Journal, vol. i. p. 310, and vol. ii. p. 108. 



