no EOYAL SOCIETY OF CANADA 



clearly the smoothing out of the shorter oscillations, together with the 

 diminution of range and the retardation of phase with increasing depth. 

 The phenomenal heat waves commencing May 4th and Sept. 23rd, are 

 traceable at a depth of 4(1 inches, but have practically disappeared at a 

 depth of (;6 inches. 



Annual Mean Temperature of the Soil. 

 The annual means for the different thermometers are as follows : — 



At first sight these are somewhat discordant, but the disagreement 

 vanishes when we consider that the readings are taken once daily at 

 Oh. 30m. p.m. At this time of day, the 20 inch thermometer is nearly at 

 its diurnal maximum, the 10 in. nearly at its minimum, the 4 in. just 

 above its mean temperature, and the one in. nearly at its maximum. 

 The probable mean temperature at each depth is 47-0°F. The mean air 

 temperature at 12-30 p.m. is 48-8°r. The annual mean air temperature 

 of the whole day taken from the ol>servatory records is 42-63°F. 



That the annual mean temperature of the soil is nearly 5°r. above 

 the mean temperature of the air, is probably due to the protective effect 

 of the snow during the winter months. We ho])e to work out and com- 

 pare the values for the different seasons ; the chief difficulty is to allow 

 for the etfect of retardation of phase at different depths. In taking the 

 annual mean the difference of phase is immaterial. It would appear not 

 improbable that this difference of annual mean temperature may afford 

 a convenient measure of the protective influence of the snow, and will be 

 found to differ materially in different years. 



Description of the Isothermal Diagram. 



The Isothermal Diagram, Fig. III., is a continuation of that given 

 last year. It is plotted on the same scale, and includes the last two 

 months of the previous diagram. (The description of the method of 

 plotting may be here repeated). 



The abscissa of the diagram represents time, on the scale of one 

 centimetre to one week. The ordinate rejtresents depth, on the scale of 

 one millimetre to one inch. The temperature, at any depth, at any time, 

 is shown by drawing the isothermal lines for each degree Fahr. This 

 is probabl}^ the mo.st convenient way of showing the whole atone glance. 

 The isothermal lines are plotted by drawing, from the observations for 

 each day, the curve showing the variations of temperature with depth. 

 From these curves it is easy to find the depth co)'responding to each 

 degree of temperature. 



