THE 



GARDENER'S MAGAZINE. 



JANUARY, 1836. 



ORIGINAL COMMUNICATIONS. 



Art. I. On the relative Temperatures of the Earth, under Surfaces 

 covered with a Vegetable Coat, and under Surfaces preserved bare j 

 •with a Table of Observations. By Robert Mallet, Esq. 



T-HE following table contains the results of a series of morning 

 and evening observations, continued for about a month, in order 

 to determine whether, and how far, the temperature of the earth's 

 surface is affected, at small depths, by the vegetation which sub- 

 sists upon it. It is uncertain whether the results observed are 

 due merely to differences of radiating and absorbing power, or 

 to some specific consequences of vegetable life. 



Two Fahrenheit's thermometers of considerable delicacy, 

 which had both been previously accurately compared, were 

 placed at about 20 ft. apart, the one beneath a surface covered 

 with a short close coat of turf or grass, and the other under a 

 portion of the soil, the surface of which was preserved bare, 

 the termination of the surface of grass being midway between 

 the two instruments. Both were so arranged, that they could 

 be examined without removal, and without danger of change of 

 temperature during observation. 



The thermometer for aerial temperature was hung at about 

 5 ft. from the ground, in the immediate neighbourhood of the 

 two terrestrial instruments ; and it was shaded so as to prevent 

 any effects from sun heat, or from radiation from surrounding 

 bodies, as far as possible. 



The table sufficiently explains its own nature. The hours of 

 9 A. M. and 8 p. m. were chosen, chiefly because they are nearly 

 those of diurnal mean temperature, and partly as a matter of 

 convenience. 



It will be observed from the table, that, with two exceptions, 

 viz. on the 10th and 30th of July, the earth beneath the surface 

 of grass was uniformly at a higher temperature than that under 

 a bare surface, or that not covered with vegetation. 



Vol. XII.— No. 70. b 



