Section III., 1897. [ 31 ] Tkans. E. S. C 



lil. — Observations of Soil Temperatures with Electrical Resistance 



Thermometers. 



By H. L. Callendar, M.A., F.E.S., F.R.S.C, 



AND 



C. H. McLeod, Ma. E., F.E.S.C. 



(Read June 23rd, 1897.) 



In continuation of the results previously presented of the Observa- 

 tions of Soil Temperatures, taken at the McDonald Phj^sics Building, we 

 have now the records of another year to submit tx) the society, containing 

 several observations of interest, together with an account of some further 

 improvements which we have been able to make in the apparatus. 



Annual Curves of Temperature. (Fig. I.) 



The annual curves of temperature for the seven buried thermometers, 

 are exhibited on a uniform scale of two centimetres to ten degrees 

 Fahrenheit. A study of these curves reveals the same peculiarities as 

 those of last year, but modified by the different conditions of the winter. 

 Owing to the absence of a protective covering of snow, during the early 

 part of the winter, the frost penetrated very much deeper into the soil 

 than in the two previous years. The thawing through of the ground, 

 after the disappearance of the snow, was also a correspondingl}^ lengthy 

 process. The time occupied was more than twenty days from the dis- 

 appearance of the snow, and the temperature at a depth of 20" did not 

 rise above the freezing point until the first of May. It is probable that 

 this circumstance may partly account for the lateness of the spring. 



A very striking and peculiar bi-eak is shown in the curves of the 20", 

 40" and QQ" thermometers, about the date November 2'7th and 28th, 

 1896. This was due to the very rapid percolation of a large quantity of 

 water at 32 ° F.. which had accumulated in consequence of a sudden thaw 

 over a thin surface layer of ice. A similar case was recorded on December 

 12th, 1894, but the present instance is a much more striking example of 

 the great influence of percolating water in causing the diffusion of heat 

 through the soil. 



