280 Mr. Lubbock on the Heat of Vapours, $c. 



value to well-regulated ascents, in which every effort should be 

 made to reach the highest possible altitude, and of course simulta- 

 neous observations should be made at the earth's surface at such 

 short intervals of time that every observation of the aeronaut may 

 be comparable with a similar observation at the surface of the earth. 

 As, however, the density and temperature of the atmosphere above 

 the height of five miles from the earth's surface can never be the 

 subject of direct experiment and observation, the observations which 

 can be made upon the conditions of steam and other vapours will 

 always maintain an indirect importance from the light which they 

 throw upon the conditions of the atmosphere. I do not think that 

 an examination of observations made in aerostatic ascents will ever 

 furnish a sure guide to the relation sought between the temperature 

 and the pressure, although if such a relation is furnished by theory 

 and corroborated by observations of other vapours, (which can be 

 carried through a greater extent of the thermometric scale, and, 

 above all, through the low pressures where the variations of tem- 

 perature become more rapid,) the obervations of aeronauts may 

 serve to determine with sufficient accuracy the constants involved in 

 the formula for atmospheric air. 



The following table*, calculated by Mr. Russell, shows the den- 

 sity and temperature of the air at different altitudes, calculated by 

 means of my expressions and with the constants 



7= 1-5, E- - 1-192: 



* In calculating this table, the law of Marriotte and Gay Lussac, expressed by the 

 equation p = fr f ( 1 + 0), 



has been implicitly supposed to hold good throughout: this of course is only conjectural, 

 and it is not intended to attach precision to the temperatures assigned to the great alti- 

 tudes. 



[To be continued.] 



