410 Prof. De Volson Wood on 



This gives 



Height, 

 miles. 



t, absolute. 



Fahr. 



scale. 



Grlaisher's 

 observations * 







520° F. 



59° F. 



59° F. 



1-5 



518 



57 





2-5 



515 



54 





3-5 



513 



52 





4-5 



512 



51 



ijjf. 



1 



510 



49 



41 



2 



501 



40 



32 



3 



493 



32 



18 



4 



484 



23 



8 



5 



475 



14 



- 2 



6 



467 



6 





7 



458 



- 3 



-11-8 



50 



212 



-249 





75 



136 



-325 





100 



87 



-374 





120 



65 



-396 





150 



36 



-425 





224 



9 



-452 





The temperatures given in twenty-five or more reports of 

 balloon ascensions, not only give values the mean of which 

 is fairly represented by the celebrated seven-mile ascent of 

 Mr. Glaisher, but his figures, given in the fourth column of 

 the table, represent a more uniform law than is common in 

 such reports. Our computed values exceed his observed 

 values at all points except at the surface of the earth, where 

 they agree. In this ascent he reached the point of freezing 

 at the height of two miles, which is lower than the average, 

 as determined by many observations; and therefore it appears 

 that equation (31) probably represents the general law better 

 than this single set of observations. The effect, however, of 

 the exponential law is scarcely perceptible within the limits 

 of observation ; for the exponent of e is so small for eleva- 

 tions under seven miles, that it makes the law of decrease of 

 temperature nearly uniform with equal increments of eleva- 

 tion. Thus, omitting fractions, the computed decrease for 

 the first mile is 10°, and the average for seven miles is nearly 

 li° ; but to assume a uniform decrease throughout the column 

 limits the height of the column independently of pressure or 

 other conditions, for it could not extend beyond the point of 

 absolute zero. There is no objection to applying such a law 



* ' Travels in the Air/ by James Glaisher, F.R.S., p. 50. 



