AS DETERMINED BY FIVE PLATINUM-RESISTANCE THERMOMETERS. 
253 
but as we are here dealing with the observations of a single year, it would be unsafe 
to attach much importance to results deducible from the smaller terms. 
The accuracy with which the observations are represented by the first three 
terms of the formulse is shown by the following table, which contains the 
differences between the mean monthly temperatures as computed and those actually 
observed ; — 
Comparison of Computed and Observed Mean Monthly Temperatures, C—O. 
Thermometer. 
1 
o 
3 
4 
5 
January . . . 
- 0°78 
- 0°86 
- 0’55 
- 0°-32 
o°-oo 
February . 
-0-17 
-0-18 
+ 0-07 
+ 0-15 
+ 0-05 
March .... 
+ 0'65 
+ 0-71 
+ 0-48 
+ 0-22 
+ 0-02 
April .... 
- 1-28 
-0-70 
-0-48 
-0J9 
o-oo 
May .... 
+ 1-56 
+ 0-91 
+ 0-25 
+ 0-01 
-0-05 
June .... 
- 113 
-1-02 
-0-52 
-0-24 
-0-02 
July .... 
+ 0-93 
+ 1-15 
+ 0-91 
+ 0-49 
+ 0-06 
August . . . 
- 1-23 
-M0 
-0-44 
-0-07 
+ 0-10 
September 
+ 0-58 
-0-15 
-0-69 
- 0-65 
-0-23 
October . 
+ 1-51 
+ 1-87 
+ 1-29 
+ 0-73 
+ 0-07 
November . . 
-3-03 
-2-14 
- 1-07 
-0-31 
+ 0-18 
December . . 
+ 2-41 
+ U52 
+ 0-75 
+ 0T8 
-0-18 
It thus appears that while the three deeper thermometers are fairly well repre¬ 
sented by the formulae, there are considerable differences in the two upper ones. 
This, especially in the case of No. 1, is largely due to the diurnal variations which 
make themselves felt to a depth of about 3 feet. 
The surface of the ground in the neighbourhood of the spot where the ther¬ 
mometers are sunk, being approximately level and the gravel being, as far as we 
know, of a fairly uniform character for a considerable distance in all directions, the 
How of heat will be represented by Fourier's equation 
k (Pd/dx 1 — dO/dt .(e) 
in which k denotes the diffusivity of the gravel, and x denotes the depth of a 
thermometer below the surface. 
A solution of this is 
6 — 2A„e - “"* sin ( n\t + (3 n x + y) 
if a* — 0 and 2 a„(3 n K = — n\. 
V mr 0 
~ 
Comparing this expression with the series (d) given on page 249 we have 
P„ = A n e~ a ^ and E,, = (3„x + y. 
