Section III., 1896. [ 109 ] Tbans. R. S. C. 



VIII. — Observations of Soil Ternper attires ivith Electrical Resistance 



Tliermometers. 



By Hugh L. Callendar, M.A., F.E.S., F.E.S.C. 



AND 



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



(Read May 22, 1896). 



The following results are communicated in continuation of a report 

 presented to Section III., in May, 1895, and published in the transactions. 



The instruments and the method of taking observations have already 

 been described in the previous communication. There is little to add 

 except that the insulation of the thermometers has remained practically 

 perfect, and that we may novv conhdently expect them to give reliable 

 results for many years to come. 



As the result of a series of observations extending over a period of 

 more than a year and a half, and including two winters, we are now able 

 to exhibit the complete annual curves for the different thermometers, 

 and to deduce the yearly averages and ranges of temperature at different 

 depths. We are also able to confirm many of the conclusions previously 

 arrived at in a more certain manner and to compare the phenomena at 

 different seasons of the year. 



Annual Curves op Temperature. (Fig. I.) 



The annual curves of temperature for the eight thermometers are 

 exhibited on a uniform scale of one centimetre to four degrees Fahrenheit 

 in Fig. I. The curve marked " Air Thermometer " gives the daily 

 variations of the electi'ical thermometer exposed to the air in a screen at 

 a height of four feet. These observations w^ere taken at 12.30 p.m. each 

 day. For comparison a curve showing the mean air temperature for the 

 whole day has been plotted on the same scale from the observatory 

 records. The vai'iations of temperature from day to day are seen to 

 extend to a depth of 20 inches in the soil. For the curves to this depth, 

 a line representing the mean temperature for each period of ten days 

 has accordingly been plotted as a guide to the eye in following the 

 variations. 



With respect to the buried thermometers, the most remarkable 

 feature of the curves is the extreme steadiness of the temperature 

 throughout the w^inter. This is due to the protective effect of the snow 

 covering, and is followed by an extremely rapid rise as soon as the snow 

 disappears and the ground is thawed. The curves also illusti"ate very 



