PROFESSOR FORBES ON THE TEMPERATURE OF THE EARTH. 



191 



the very intelligent gardener at Raitli ; 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. 



January... 

 February . 

 March .... 



April 



May 



.Tune 



July 



August.... 

 September 

 October ... 

 November 

 December. 



Mean of whole Year 



1 Foot. 



33° 

 33 



35-0 

 39-7 

 44-0 

 51-6 

 54-0 

 50 '0 

 51-6 

 47 

 40-8 

 35-7 



43-8 



2 Feet. 



36°-3 

 36-0 

 36-7 

 38-4 

 43-3 

 50-0 

 52-5 

 52-5 

 51 -3 

 49-3 

 43-8 

 40-0 



44-1 



4 Feet. 



40°-7 

 39 

 39-6 

 41-4 

 43-4 



47-1 

 50-4 

 50-6 

 51 '8 

 49-7 

 46-3 



43-0 



45-1 



8 Feet. 



43°0 

 42-0 

 42 '3 

 43 '8 

 44-0 

 45-8 

 47-7 

 49-4 

 50-0 

 49 -6 

 45-6 

 46-0 



46-0 



1 Foot. 



35°- 6 



37-0 



39-4 



45-0 



46-8 



5i 



55 



53 



1 



2 



4 

 53 -0 



45 

 41 



37-9 



1817. 



2 Feet. 



38°-7 

 40-0 

 40-2 

 42-4 

 44-7 

 49-4 

 55 

 53-9 

 52-7 

 49 -4 

 44-7 



i Feet. 



40-8 



44-9 



45-9 



40°- 5 

 41-6 

 41-7 

 42-6 

 44 -6 

 47-6 

 51-4 

 52 

 52-0 

 49 4 

 47-0 

 44-9 



46 -2 46 -6 



8 Feet. 



45°- 1 



42 



42 



42 



44 



47-8 



49-6 



50 



50-7 



49-8 



47-6 



46-4 



" If 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 gi-eenstone rock." 



I had intended to have engraved the curves of the course of temperature from 



