Weights and Measures of New York. 105 



ture, independent of the indications of instruments that, in the 

 improvement of science, may become obsolete, and constant 

 in all varieties of physical circumstances. Such a temperature 

 is marked in nature while the process of liquefaction is going 

 on, or what is commonly called the freezing point of water. 

 This, therefore, should be declared, in the new law, to be the 

 temperature at which such comparisons should be made, or to 

 which they should be reduced. 



The extension in length of the unit of lineal dimension will 

 furnish the elements of measures of a larger size ; its square, 

 or that of one of its multiples, will be the unit of superficial 

 measure, and its cube of solid. 



To determine the unit of weight, it will be necessary to have 

 recourse to some fluid that can at all times, and under all cir- 

 cunr tances, be obtained pure and homogeneous. Distilled 

 water is a fluid of this nature, and the law should declare that 

 the weight of a certain bulk of it shall be equal to a certain 

 defined proportion, or multiple of the unit of weight. To 

 make this declaration specific, the circumstances under which 

 the comparison is to be made, must be declared in the law ; for 

 water, like all other substances, will be of different weights 

 under equal bulks, at different temperatures ; and its apparent 

 weight will be affected by the varying pressure of the atmos- 

 phere, as well as that of the weights employed, while their 

 absolute gravity is that they would possess in vacuo. There 

 appears at first sight to be a practical difficulty in this determi- 

 nation, in consequence of its being almost impossible to ascer- 

 tain with the necessary precision the interior dimensions of a 

 vessel ; but we have a remedy in the well-known physical fact, 

 that a solid body loses, when weighed in a liquid, a portion of 

 its weight of an equal bulk of the liquid; and the exterior 

 dimensions of a regular solid are determinable within the requi- 

 site limits. But this experiment will be affected by the calorific 

 expansion of the substance employed, and by the buoyancy of 

 the air affecting its absolute weight. The law then must not 

 only express the absolute weight (in vacuo) of a certain bulk 

 of water in terms of the standard of weight, but must describe 

 the temperature of the water, and the substance of which the 

 weights and the experimental solid are to^be made. It so 



