336 Bottom Heat. [Dec, 



earth may be taken as on an average, 5 deg. above the mean 

 temperature of summer in warm countries; very often more, sel- 

 dom less; so that if the mean temperature of Rome in the hottest 

 month is 77 deg., it is probable that that of the soil, at the same 

 time, will not be less than 82 deg. As we advance to the north- 

 ward the difference diminishes, so that in London it is not more 

 than 2 deg. in favor of the earth. 



The correctness of this mode of computing terrestial tempera- 

 ture is borne out by the two best sets of observations that we have 

 from hot countries. Captain Newbold's observations (Philosoph- 

 ical Transactions, 1845) at Bellary, on the centre of the table 

 land of peninsular India, in lat. 15 deg. 5 min. N., and 1,600 feet 

 above the level of the sea, are as follows: In the hot month of 

 May, sky unclouded, soil reddish and light in texture, and com- 

 pletely sheltered by a thatched roof, the temperature of the soil at 

 a foot below the surface was found to be as follows: 



The mean temperature of the place about 80O5. 



This is confirmed by the results of an invaluable set of daily 

 observations for three years, made at Trevandrum, in India, by 

 John Caldecott, Esq., Astronomer to the Rajah of Travancore, and 

 lately published in the " Transactions of the Royal Society of Ed- 

 inburgh" vol. 16, p. 379. Professor Forbes has reduced them 

 to the following table: 



