]^ M. vg^^pkimus on the Moving Fwce /tfll^i, 



existing at the time; with proportionately greater tenBion^Sttei 

 numbers were too large. The case, however, is not finally set at 

 rest by these experiments ; for, as remarked by Regnault, it is 

 doubtful whether the divergence is due to the too great specific 

 heat of the developed vapour, or to a quantity of water condensed 

 upon the sides of the glass balloon. Other experiments, wherein 

 the vapour was not developed in vacuo but saturated a current qf ^ 

 air, gave results which were tolerably free* from these irregulaii-^' 

 ties ; but neither from these, however important they may be in • 

 other respects, can a safe conclusion be di'awn as. to the depprt^t 

 ment of the vapour in vflCMO. '*'"'-"« > \ 



The following considerations will perhaps feeiliB' to fill up to" 

 some extent the gap caused by this uncertainty. The table (IV.) 

 shows that the lower the temperature of the vapour at its max- 

 imum density, the more nearly it agrees with the law of M. and^ 

 G. ; and hence we must conclude, that the specific weight foi'" 

 low temperatures approaches more nearly the theoretic value 

 than for high ones. If therefore, for example, the value of 0*622 

 for 0° be assumed to be correct, and the corresponding values d 

 for higher temperatures be calculated from the following equa- 

 tion deduced from (26.), i -^ \s 



^Ai iai t focrao 



m—ne 



n 



Ttf 



^rf rijso \8v 



tazo 



we shall obtain far more probable values than if we had majflrr 

 use of 0*622 fpr. ^11. temperatures. The follo;\vipg table gives 



some of these. 



Table V. 



ili morii baa 



Strictly speaking, however, we must proceed still further. In 



Table III. it is seen that the values of Ap{s—(r) — -— , as tli^,;j. 



temperature decreases, approach a limit which is not attained^ * 

 even by the lowest tem])eratures in the table; and not until this ' 

 limit be reached can we really admit the validity of the law of ?. 

 M. and G., or assume the specific weight to be 0*622. The 

 question now occurs, what is this limit ? Could we regard the 

 formula (26.) to be true for temperatures under —15° also, it 

 would only be necessary to take that value to which it approaches 

 as an asymptote, tw =31*5 19, and we could then set in the placets 



,.,{ ♦ Anv. de Chim. et de Phys., 3 ser. vol. xv. p. 148. r ni nfia 



