
OBSERVATIONS OF UNDERGROUND TEMPERATURE. 423 
tion do not exceed the probable errors in the data of observation sufficiently to 
allow us to draw any reliable conclusions from their apparent values. 
TABLE XI.—AVERAGE SEMI-ANNUAL HARMONIC TERM, FROM EIGHTEEN YEARS’ 
OBSERVATIONS AT CALTON HILL. 


Depths below sur- A, B, Amplitudes Kpochs in degrees 
face, in French feet.| In degrees Fahr. In degrees Fahr. In degrees Fahr. and minutes. 
3 feet. °1518 °-5842 °-604 roa 
6 feet. 0461 *3911 394 96 43, 





The ratio of diminution of the amplitude here is ae or 1°53, of which the 
Napierian logarithm is -426. Dividing this by 3, we find 
142 
as the rate of diminution of the logarithmic amplitude per French foot of descent. 
The retardation of epoch shown is 21° 17’; and therefore the So un per 
French foot of descent is 7° 6’, or, in circular measure, 
1239. 
If the data were perfect for a periodical variation, and the conditions of uniformity 
Supposed in Fourier’s solution were fulfilled, these two numbers would agree: 
and each would be equal to fe ih, Hence, dividing them each by 1/2, we find 
Apparent values of sie 
100 (by amplitudes) 
877 (by epochs). 
The true value of dh - must, as we have seen, be *116, to a very close degree of 
approximation. 
30- When we consider the character of the reduction we have made, and 
remember that the data were such as to give no semblance of a theoretical agree- 
ment when the first five years’ term of observations was taken separately, we 
may be well satisfied with the approach to agreement presented by these results, 
depending as they do on only eighteen years in all, and we may expect that, when 
the average is of a still larger term of observation, the discrepancies will be much 
diminished. In the mean time, we may regard the semi-annual term we have 
found for the three feet deep thermometer as representing a true feature of the 
_ yearly vicissitude; and it will be surely interesting to find whether it is a con- 
stant feature for the locality of Edinburgh, to be reproduced on averages of sub- 
sequent terms of observation. 
34. It may be remarked, that the nearer to the equator is the locality, the 
