UNITS AND STANDARDS OF MEASUREMENT. 373 



weighing against water, they will not agree very closely 

 with each other ; and, as a matter of fact, the two principal 

 standard kilograms neither agree with each other, nor 

 with their true definition u . The so-called Kilogram des 

 Archives weighs 15432*34874 grains according to Prof. 

 W H. Miller, while the kilogram deposited at the 

 Ministry of the Interior in Paris, as the standard for 

 commercial purposes, weighs 15432*344 grains x . 



Now since a standard weight constructed of platinum, 

 or platinum and iridium, can be preserved in all proba- 

 bility free from any appreciable alteration, and since it 

 can be very accurately compared with other weights, we 

 shall ultimately attain the greatest exactness in our 

 recorded measurements of weight and mass, by assuming 

 some single standard kilogram as a provisional standard, 

 leaving the determination of its actual mass in units of 

 space and density for future investigation. This is what 

 is practically done at the present day, and thus a unit of 

 mass takes the place of the unit of density, both in the 

 French and the present English systems. The English 

 pound is defined by a certain lump of platinum, carefully 

 preserved at Westminster, and is an entirely arbitrary- 

 mass, made to agree as nearly as possible with old English 

 pounds. The gallon, the old English unit of cubic mea- 

 surement, is defined by the condition that it shall con- 

 tain exactly ten pounds weight of water at 62 Fahr.; and 

 although it is stated that it has the capacity of about 

 277-274 cubic inches, this ratio between the cubic and 

 linear system of measurement is not legally enacted, but 

 is left open to investigation from time to time. While 

 the French metric system as originally designed was 

 theoretically perfect, it does not seem to differ practically 

 in this point from the English system. 



u Thomson and Tait's 'Treatise on Natural Philosophy,' vol. i. 

 p. 325. * ibid. 



