THE ART OF WEIGHING AND MKA.'^rL'ING. 



628 



will be to regard tlic entire set as a standard oC r}\2 troy ounces. In 

 tbat case the sninniation of the several coluuius gives 



512 ounces = 128 x + 39 grains. 



whence 



X = 4 ounces — 0.3047 grain (2) 



and by snbstitnting tbat value in the equations (1) we obtain the cor- 

 rections to the several weights given iu the second column of Table I. 



Taule I.— Cokukctioxs to the Exchequek Staxdard Tuov Weights of 1588, 

 Deiuved from the Weighings made by Messrs. Harris and Chisholm. 



From equations (1) and (2) we have 



4 ounces = 4-oz. weigbt + 0.5547 grain. 

 8 ounces = 8-oz. weigbt -f 0.3594 grain. 



whence it follows that the sum of the 8 and 4 ounce weights, which 

 constituted the Exchequer standard troy pound, was too light by 

 0.914L of a grain. As the mean correction obtained from the four 

 weights belonging respectively to the Mint and to Mr. Freeman, agrees 

 closely with this result, the true correction to the Exchequer standard 

 must have been very approximataly 1 grain ; and in adopting 1^ 

 grains the committee seem to have augmented the weight of the troy 

 pound by about one-quarter of a grain. The corrections which result 

 to the Exchequer troy weights upon the committee's assumption that 

 the sum of the 8 and 4 ounce weights was 1^ grains too light are given 

 in the third column of Table I; while the fourth column contains the 

 corrections found by Mr. Cliisholm in 1873, * and the fifth column shows 

 the loss of weight which occurred between 1758 and 1873. In view of 

 the fact that these weights were constantly used for comparing local 

 standards during a period of no less than two hundred and thirty seven 

 years, from 1588 to 1825, their excellent preservation is very remarkable. 

 In the rei)ort of the committee of 175S there is another set of com- 

 parisons of the Exchequer troy weights, t said comparisons haxing 

 been made on April L4, 1758, in accordance with the directions of 



'50, p. 21. 



1 13, p. 435. 



