130 DR. WM, THOMSON ON THE CONVECTIVE EQUILIBRIUM 



heat of a stated weight of vapour^ than from any direct 

 experiments on the density of vapour made up to that 

 time. This conclusion has been verified by the recent 

 experiments of Messrs. Eairbairn and Tate. With the 

 assistance of some excellent tables in Rankine's " Steam 

 Engine and other Prime Movers/' calculated on these prin- 

 cipleSj I have obtained the following results : — 



ss 



of air 

 17 lbs. 

 oot. 



ue of 

 cubic 

 ited 



ate 



bulk 



apour 



fele- 



rature. 







om 

 e re- 

 moist 

 nt. 



Temperatu 



Centigrade, 



^-273-7. 



Volume of 1 lb 



at pressure 21 



per square f 



Dynamical va] 



latent heat of 1 



foot of satur 



vapour. 



Proportion 



diminution of 



of saturated v 



per 10 Cent. 



vation of tempe 



Augmentatio 



volume of 1 1 



moist air requi 



cool it 10 Ct 



Elevation fr 



earth's surfac 



quired to cool 



air by 1° Ce 









d loq s 



dv 



dx 



^-273-7 



V 



JL 















—dt 



—dt 



—dt 





cubic ft. 



ft. lbs. 





cubic ft. 



feet. 



o 



12-38 



249 



•0698 



•1905 



499 



5 



I2"6l 



348 



•0671 



•2150 



551 



lO 



12-83 



481 



•0644 



•2434 



611 



15 



13-06 



655 



•0617 



•2753 



678 



20 



13-29 



881 



•0592 



•3096 



751 



^5 



i3'52 



1171 



•0569 



•3455 



827 



30 



1374 



1538 



•0546 



•3800 



900 



35 



i3'97 



1999 



•0524 



•3950 



932 



The column of this Table headed 



dv 



dt 



is calculated 



from the preceding formula. It expresses the expansion 

 on the bulk of a cubic foot required to produce a cooling 

 effect —dt (along with an infinitesimal lowering of pres- 

 sure below the standard pressure of 21 17 lbs. per square 

 foot^ denoted hj p), when the mass is not allowed either 

 to absorb or to emit heat. 



(dx \ 

 headed — 3-, ) is calculated from the 



dv 

 column headed — -r. by the following formula, 



dx=pdv-\-pv 



— dt 



