ON A GAUGi: I'Olt .SMALL .SClUiU'S. 



0<7 



Second Report of the Committee, coiisiHtiiuf of Sir Joski'II Wfiit- 

 vvoRTii, Sir W. Thomson, Sir F. .1. Bkamwell, Mr. A. Stkoii, .Air. 

 Beck, iNIr. W. \{. Phkkci;, jSIr. E. Crompton, Mv. K. \\\v,Vr 

 {Secretary), ?tlr. A. Le "Sv.w. Foster, Mr. liATiMEit Clark, INIr. 

 H. Truemax Wood, and Mr. Buckney, appointed for the puvpo><e 

 of determuilnf/ a Ganyefor the manufacture of the vavioitu smaJl 

 Screws used In Telei/raphlc and Electrlad Appavatas, hi Clock- 

 work, and fi)i' other analo(/oiisi pnrpose-'^.^ 



1. Since tlio jiveseritation ot" its first Report on a flange for small 

 screws at the nicetinu' of the Association held in 188:2 at Southaniptiui, 

 this Committee has furtlier examined into tlie rocoinmciuhitions there 

 made, with the result that they now have to proj)ose some iinjiorliint 

 moditications, the general eH'ect of which will, it is felt, be to materially 

 facilitate the introduction of the system. 



2. The want of unanimity on the jiart of the Committee rel'tirred to 

 in paragraph 7 of that Report arose mainly on the question as to whether 

 the inch or millimetre should be ta^:en as a unit of measurement. It is 

 evident that if either is rigidly adhered to, and in any way em[)!oyed 

 in the nomenclature of the screws, as, for example, in s[)ecit'ying the 

 diameter, pitch, or threads per inch or ])er mm., the same dimensions 

 could not be expressed in whole numbers in the other unit, and thus a 

 material obstacle would bo at once introduced to its general adoption, 



3. Ifc should be pointed out, however, that it has hitherto been the 

 common practice to designate such small screws as the Committee alone 

 is considering, not by any speciiic dimension, but by a number, whieii as 

 a rule is arbitrarily chosen and does not of itself form a guiile to the 

 size of the screw. Considering, then, that the unit of measurement is 

 only indirectly connected with the subject of a screw gauge, the Com- 

 mittee has felt that the two units might be reconciled so far as relates 

 to snch a subject, and that thus one important dilliculty would be 

 removed. 



4. The manner in which the series of screws ado])ted lately by Swiss 

 manufacturers is correlateil hiis been sulHciently explained in tho 

 ju-evions Report, and very full explanations are given in the two original 

 pamphlets to which reference is there made.'^ The diameter (I)) is 

 related to_ the pitch (P) l)y tho formula I) = G P'.;, (IV all nieasure- 

 raents being in millimetres, and P having succe':iively tho values 

 1 (or 0-9") nnn.; O'J' mm. ; O'U'^ mm.; 0-!l'' mm. . . . O'O" ram. 



Thus n, the index, becomes a convenient designating number for the 

 screw, and the formula (1) may be expressed 1) = G (O'.)")';, whero 



•). Tho pitch of any screw can be at once ascertained from its desig- 

 nating number by raising Ot> to tho [lower indicated by that number; and 

 from this pitch the diameter is direct ly deducible by the formula ( I ), so that 

 the number (-«.) given in tho first column of the table, by which a screw 

 is kt\()wn, is intimately related to all its dimensions. 



' Sco Hcpon f)l' tlio Coinicil presented to tlin General Conmiittee .-it Montreal. 

 • Sijxthuatiqur dcK rh Ilorloiftrci, hy I'rof. M. i Iniry, (leneva, 1878. .\oth'v »ur Ic 

 •'^i/ntiinc dcH vis (ic la Filiirc Siiisie, tieneva, 1880, by tiie same author. 



