Secrion III., 1895. [68] [TRANS RSC: 
V.— Preliminary Results of Observations of Soil Temperatures with Electrical 
Resistance Thermometers, made at the McDonald Physics Building, 
McGill University, Montreal. 
By Huan L? CALLENDAR, M.A., F.R.S., McDonald Professor of Physics. 
(Read May 15, 1895.) 
The following series of observations of soil temperatures with buried 
thermometers was undertaken in continuation of some experiments made 
by Prof. D. P. Penhallow and Prof, C. McLeod, of McGill University. 
Prof. Penhallow made an extended series of such observations during 
the years 1882-1883, in the summer months, with mercury thermometers 
of special design. These observations could not conveniently be con- 
tinued through the winter. An attempt was accordingly made at the 
McGill College observatory, in conjunction with Prof. McLeod, to replace 
the mercury thermometers by thermocouples. This admitted of read- 
ings being taken indoors without disturbing the buried instruments, but 
in spite of every precaution in fitting up the thermocouples and in taking 
the observations, the indications were not found to be sufficiently accu- 
rate. 
In transferring the site of the observations to the McDonald Physies 
Building, it was accordingly decided to try a set of electrical resistance 
thermometers in place of thermocouples. The instruments were obtained 
and placed in position in the month of October, 1894. Observations have 
been taken continuously since that date. It is not yet possible, from so 
limited a series of observations, to deduce many results of general im- 
portance, but a description of the method and of the results so far 
obtained will serve to show the special applicability of this type of ther- 
mometer to the determination of soil temperatures, and to indicate the 
direction in which further experiments may be made. 
DESCRIPTION OF THE INSTRUMENTS. 
The thermometers were made of the usual pattern by the Instru- 
ment Company, Cambridge, England. Each instrument consists of a 
carefully insulated coil of platinum wire about three inches long, pro- 
tected by an external tube of glass or copper about half an inch in dia- 
meter, and connected to the indicating apparatus by insulated copper 
leads, which may be of any convenient length. The indicating appa- 
ratus in the present case was placed inside the building at a distance of 
about 120 feet from the thermometers. It consists of a specially con- 
