[ 194 ] 

 XXXIII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 145.] 



June 12, 1856. — The Lord Wrottesley, President, in the Chair. 



THE following communications were read : — 

 "On the Construction of the Imperial Standard Pound, and its 

 copies of Platinum ; and on the comparison of the Imperial Standard 

 Pound with the Kilogramme des Archives." By W. H. Miller, 

 M.A., F.R.S., Professor of Mineralogy in the University of Cambridge. 

 —Part II. 



The Quartz Weight 

 The hardness of quartz, its capability of taking a high polish, the 

 absence of any hygroscopic properties, and its indestructibility at the 

 ordinary temperature of the atmosphere by any chemical agent ex- 

 cept hydrofluoric acid, are such valuable qualities in a substance 

 used for the construction of weights, that Professor Steinheil adopted 

 it as the material for a copy of the kilogramme. The only objection 

 to the use of a weight made of quartz is, that on account of the 

 large amount of air displaced, the barometer and thermometer must 

 be observed with extreme care during its comparison with a weight 

 made of any ordinary metal. The Committee commissioned Mr. 

 Barrow to construct a weight of quartz sufliciently near to 7000 grs. 

 to admit of readily deducing the pound from it. Its form is that of 

 a cube of about 2' 2 inches, having its edges and angles rounded. 

 Its apparent weight in air is intermediate between that of a pound 

 of platinum and a pound of brass, approaching more nearly to the 

 latter than to the former. 



Six series of weighings in water gave for the absolute weights of 

 water displaced by it at 18° C. — 



2639-831 



2639-809 



2639-838 



2639-825 



2639-819 



2639-814 



Mean .... 2639-823 

 Whence density quartz at 18° C. ^ 2-652590. 



density water at 1 8C 

 Denoting the quartz weight by Q, and the new Imperial Standard 

 Pound by I, the comparisons of Q with I in air, reduced to a 

 vacuum, gave 



Grains. No. of Obs. 



Q= I 4- 2-36801 40 



Q = I + 2-36871 40 



Q = I + 2-36817 40 



Q = I + 2-36782 40 



Q= I + 2-36715 40 



Mean Q = I + 2-36797 200 



