• 106 Professor Renwick on the 



happens, that in this case also we have a temperature, or rather 

 a state of Avater, defined by a physical fact independent of 

 instruments or extrinsic causes. Water does not follow the 

 general rule of contraction, by diminution of heat at all tem- 

 peratures, but, after contracting to a certain limit, again expands 

 while cooling for several degrees above its freezing point. 

 This fluid, therefore, has a maximum of density, and varies so 

 slowly in bulk on each side of this maximum, as to afford room 

 for the greatest accuracy of experiment. 



Two methods exist of defining the magnitude of measures 

 of capacity. The first and most obvious would be to prescribe 

 the cubical dimensions of the unit in terms of the unit of 

 length; but this is liable to the objection already stated, viz., 

 the great difficulty of ascertaining with accuracy the internal 

 dimensions of a vessel ; the second consists in prescribing the 

 weight of water that the measure shall hold, and this is in all 

 respects preferable, but especially so from the very great ease 

 with which the determination can be made. Here also it will 

 be necessary to declare the atmospheric pressure and tempera- 

 ture at which the experiment shall be made, and this may be 

 simply done by enacting that the water shall be at its maximum 

 density, and pressure of the atmosphere at a mean. 



(4.) The law of the province of New York of 1703, the 

 act of 1784, and the revised law of 1813, recognise two 

 standards of weight, without prescribing their relation to each 

 other. Of these, the troy pound has long ceased to be used 

 in any purely mercantile transaction, except in the retail trade 

 of the apothecary ; gold and silver are indeed also weighed by 

 the troy pound : the former object is of very trifling importance, 

 and the latter being governed by the practice of the mint of 

 the United States, may be considered as a subject on which the 

 national government has virtually legislated, and on which it 

 would be improper for the state government to act. No other 

 unit of weight then should be retained but the avoirdupoise 

 pound ; and as the quintal of 112lbs. has been abolished in 

 practice, no other denomination of that species of weight, 

 except the usual binary subdivisions of the pound. 



Did the original law of 1703, or the act of 1784, authorise 



