PROFESSOR FORBES ON THE TEMPERATURE OF THE EARTH. 



209 



Also px, ^01, Pwi\ denoting the depths corresponding to a range of 1°, 0°-l, 0°-01 

 Cent., we have 



_ A 1 + A 2 + A 



P\ — ~ -^ "o.l — — p ^001 = ■ 



B 



B 



B 



Numerical Example. By the projection for 1837, Plate IX., we find 



Observatory. 



14°^6 Cent. 



3-0 F. ft. 



1^164 

 - 0^0547 

 21-4 F. ft. 

 397 - 

 58^1 - 



The superficial range 

 jOio= depth where range = 10° Cent. 

 Whence A 

 B 



P\ 



Po-i 

 Po-oi 



The numbers in the last line may be taken (arbitrarily) as a limit of compa- 

 rison for the point at which the annual variation sensibly vanishes, and its dif- 

 ference in the thi-ee stations shews the mariied influence of the conducting soil 

 or rock. The following tables contain a summary of these results for five years. 



Table X. Shewing the Values of A and B.* 



Table XI. Shewing the Depths at which the Annual Range is reduced to 



0°-01 Cent. 



* The French foot and centigrade degree are here taken as units. 

 VOL. XVl. FAKT 11. 3 G 



