THE ART OF WEIGHING AND MEASURING. 



G25 



In addition to being less" exact, the weighings by Mr. Freeman 

 ditter from those by Mr. Harris principally in the sign of the correc- 

 tion to the o2-onnce weight; the former stating that the 32-ouuce 

 weight was lighter than the sum of all the smaller weights and the 

 latter that it was heavier. To ascertain which was right we have 

 only to compare the resulting systems of corrections with those found 

 by Mr. Cliisholm in 1S73. Table I shows that according to Mr, Harris's 

 w^eighings all the weights have grown lighter during the interval froui 

 1758 to 1873, while Table II shows that according to Mr. Freeman's 

 weighings some have grown lighter and others heavier, and that by 

 (piantities which cannot be attributed to accidental errors in the weigh- 

 ings. In view of these facts there can be no doubt that the committee 

 of 1758 was right in using only Mr. Harris's weighings, and it seems 

 equally certain that the numbers in Table I should be adopted to the 

 exclusion of those in Table II. 



Table II. — Correctioxs to the Exchequer Standard Troy Weights of IfvSS, 



DERIVED FROM the W^EIGHIXGS MADE BY MESSRS. FREEMAN AND ChISHOLM. 



Denomination of Weight. 



16 



32 



64 



128 



256 



onnce solid .. 

 ounce hollow 



ounce 



onuce 



ounce 



ounces 



ounces 



ounces 



ounces 



ounces , . 



ounces 



ounces 



ounces 



Sums 



Apparent 

 correction in 



1758. 



Grains. 



— 0.01 

 + 0.49 



— 0.03 

 0.05 

 0.11 



— 0.21 

 + 0.08 



0.16 

 + 0. 31 



— 1.38 



— 0. 75 

 + 13.50 



— 12.00 

 j- 0.00 



From coraparisons of their troy pound with their avoirdupois pound, 

 and with the 2-marc weight sent to them by the French Academy in 

 1742, the Royal Society of London found* — 



(1) That the English avoirdupois pound weighed 7,004 troy grains : 



(2) That the French livrCj consisting of 2 marcs, weighed 7,560 

 troy grains: 



And for three-quarters of a century the latter value was universally 

 accepted. Further, when the metric system came into being the kilo- 



*7, page 187. It is usual to designate 1742 as the date of the exchange of stand- 

 ards, but the remark of Cassini de Thury (5, p. 135) shows that the true date must 

 have been prior to April, 1733. In his paper of November, 1742, Graham makes only 

 the indefinite statement that the exchange was "proposed some time since," 



H. Mis. 142 40 



