
PROFESSOR FORBES ON THE TEMPERATURE OF THE EARTH. 191 
the very intelligent gardener at Raith; and we have now before us a register of 
their variations for nearly three years. It thence appears, that, in this climate, 
and on naked soil, the frost seldom or never penetrates one foot into the ground.” 
* + * * * * 
«‘ These observations are quite satisfactory, and exhibit very clearly the slow 
progress by which the impressions of heat or cold penetrate into the ground. It 
will not be far from the truth to estimate the rate of this penetration at an inch 
every day. The thermometers hence attained their maximum at different periods, 
though in a tolerably regular succession. ‘The mean temperature of the ground, 
however, seemed rather to increase with the depth; but this anomaly has evi- 
dently proceeded from the coldness of the two last summers, and particularly that 
of 1816, which occasioned such late harvests and scanty crops. Thus, the ther- 
mometer of one foot indicated the medium heat of only 43°8 during the whole of 
the year 1816. But it will be satisfactory to exhibit the leading facts in a tabu- 
lar form. The following are the mean results for each month, only those for De- 
cember 1817 are supplied from the corresponding month in 1815. 
TABLE I. LESLIE’S OBSERVATIONS. 
1816. 1817. 




2 Feet. | 4 Feet. | 8 Feet. . | 2 Feet. 
January 
February 

September 
October 
SHAIDAARE RK DSH 


Mean of whole Year : : 46 -0 







“Tf the thermometers had been sunk considerably deeper, they would, no 
doubt, have indicated a mean temperature of 47°7. Such is the permanent tem- 
| perature of a copious spring which flows at a short distance, and about the same 
_ elevation, from the side of a basaltic or greenstone rock.” 
| I had intended to have engraved the curves of the course of temperature from 
