Stoney — How to simplify British Weights and Measures. 21 



Note 1. 



On Graduating Scales, and Making Screws. 



By a recent International arrangement, in which our Board of 

 Trade took part, the following relation between the yard and the 

 metre has been definitively agreed upon, viz. : — 



Old yard = 0-9143992 metre. 



This in practice is undistinguishable from 0-9144 metre, since the 

 proportional increase which is here made is but a small fraction of the 

 probable error in such determinations ; as is manifest upon comparing 

 with one another the values furnished by the best determinations that 

 have been made in Europe and America. 



Another consideration concurs in showing that the difference 

 (which is less than the millionth part of the whole length) has no 

 practical significance. It is the amount by which the length and 

 subdivisions of a bronze rule are altered when the temperature 

 deviates by less than - 2 V of a degree Centigrade from that for which the 

 rule was justified. Now the intended temperature of the original 

 bronze standard, which was destroyed in the conflagration of the 

 Houses of Parliament in 1834, and of which our present imperial 

 standards are meant to be copies, is not known to trns degree of 

 accuracy ; inasmuch as there exists no record of the kind of glass 

 used in making the stems and bulbs of the mercury thermometers, by 

 which the temperature prescribed by the Act of 1824, viz. : 02° F., 

 was determined, when those copies were made from which our present 

 standards are taken. 



Adopting then the simpler value, we find that — 

 0-9 metre (the new yard) : 0-9144 metre (the old yard) : : 125 : 127, 

 from which ratio we gain the following very valuable practical rule, 

 that Dividing Engines and Lathes which are furnished with Whitworth 

 screws the pitch of which is knoivn in old imperial measure, can be made 

 to graduate scales and make screws of equal accuracy in the new impel ial 

 measure, or in metric measure, by the simple expedient of introducing two 

 change-wheels, one with 125 the other with 127 teeth. 



Note 2. 



On the Pronunciation of the Names of Metric Weights and Measures. 



The word litre, like mitre and nitre, has come into English, 

 through the French from the Greek ; and in Greek the spelling and 



SCIENT. PROC. R.D.S., VOL. X., PART I. D 



