356 THIRD RfiVORT — 1833. 



*' The height of the mercury in the barometer, reduced to the 

 freezing point, was at the same time 332"36 French Hnes. The 

 volume of the air was in each experiment reduced to 5\%4, or 

 the pressure added to that of the atmosphere was 4*284 atmo- 

 spheres. The pressure reduced to hnes of mercury is thus, 

 S32'36 X 4"264 = 141 7* 18 ; yet this reduction was not produced 

 by the united pressure of the atmosphere and the piston alone, 

 but was aided by a pressure of 40 lines of water, whose effect 

 is equal to that of 2*94 lines of mercury, which is to be de- 

 ducted, leaving then a pressure of 1414*24. Now, when a 

 pressure of 1414-24 produces a descent of 49*96 parts, a pres- 

 sure of 336 must produce a descent of nearly 1 1 '87 parts. 

 Each part makes in the instrument here employed 3*497 mil- 

 lionths of the whole capacity. 11*87 x 3*497 gives ultimately 

 41*51. The temperature of the water was at the beginning 

 0-20 Th., at the en(,l 0*2025 Th., by the thermometer. The 

 water stood 10*1 parts, about o5 millionths, higher at the 

 end of the experiments than at the beginning. This gives 

 0*202 Th., which is as perfect an agreement as could be de- 

 sired, the difference being only 0*0005 of the thermical mea- 

 sure, or 0*09 degree of the scale of Fahrenheit. During the 

 last three months I have not made use of the tube e d for mea- 

 suring the compression of air, but I have employed a glass tube 

 LMN (fig. 2.), whose shape is better seen in the diagram than 

 it can be described. The capacity of the part above the line y, 

 and that of the whole, are measured by weights of mercury. WHien 

 the instrument is sunk in the water, the liquid mounts in the tube 

 which has the scale O, whose parts are likewise measured by 

 mercury. This has the double advantage of giving a more ac- 

 curate measure, and of showing whether or not the volume of 

 air has changed. In the series of experiments above mentioned 

 this measure has been employed. By a considerable number 

 of experiments, I have found that the compressibility of water 

 is not so gi'eat in high temperatures as in lower. Canton had 

 already obtained this result, but some doubts might remain, be- 

 cause his experiments were made by means much more trouble- 

 some to make use of, and at a time when all instruments were 

 less perfect. Here, as well as in the whole research into the 

 compressibility of water, the new experiments prove the great 

 skill and acute judgement of this distinguished philosopher. 

 My experiments are much more numerous than his, and have 

 been extended to a greater range of temperatures. Their re- 

 sults may be expressed by supposing that the pressure of one 

 atmosphere equivalent to 336 French lines' height of mercury 

 develops a heat 0*00025 Th. = 0*045° Fahr. In calculating 



