46 “ REPORT—1883. 
nearly 15 minutes, and it met with chalk mud at a depth of 1,210 feet 
from the surface of the ground. Here it was allowed to remain for 
30 minutes. It was then hauled up as slowly as it had gone down, and 
its indication was 69°°7 F. 
Observations were next taken in the same manner at two smaller 
depths, the temperatures recorded being 57° F. at 400 feet and 65°-1 F. 
at 800 feet. 
The thermometer was then lowered again to the same depth as at 
first, and showed a temperature 2°°2 higher, but the lowering and raising 
on this occasion. were hurried, as it was getting dark, and it is probable 
that the 2°-2 of excess were owing to mercury which was shaken out of 
the bulb into the stem during the hauling up. 
These observations were made on January 18. After correspondence 
with the Secretary the thermometer was again lowered to the full depth, 
and allowed to remain there fora week. It was hauled up on February 1, 
and read 69°-7—-exactly the same as in the first observation. 
By way of verifying the explanation above given of the 2°2 of ex- 
cess observed on the second occasion, Mr. Shore has tested the effect of 
shaking the thermometer by hand, and finds that he can, by a few jerks, 
cause a sufficient quantity of mercury to pass through from-the bulb to 
make this difference. 
All these observations were taken before the water had been disturbed 
by any preparations for continuing the boring, and the temperature 
69°-7 at 1,210 feet may be accepted as truly representing the temperature 
of the ground at this depth. 
The mean annual temperature of the air at Southampton, as calcu- 
lated by Mr. Shore from the daily obscrvations at the Ordnance Survey 
Office, for the ten years 1872-1881, is 50°°0 F. If we allow, in accord- 
ance with general experience, an excess of 1° in surface temperature of 
the soil, we have an increase of 18°-7 in 1,210 feet, which is at the rate 
of 1° F. in 65 feet. 
Judging from past experience, not much reliance can be placed on 
the temperatures at intermediate depths, as they are liable to be largely 
affected by convection. In the present case a comparison of the tem- 
peratures at 800 feet: and 1,210 feet gives an increase of 1° in 89 feet, 
and a comparison of those at 400 feet and 1,210 feet gives 1° in 
64: feet. 
The temperature of the surface of the water on January 18 was 55°. 
This was only 40 feet below the surface of the ground, and the tempe- 
rature of the air at the time was 49°. The surface of the ground is 
140 feet above sea-level. 
The Council of the Mining Institute of Cornwall have undertaken a 
series of observations on underground temperature in Dolcoath mine. 
The thermometers (of the usual slow-action pattern) were supplied by 
our Secretary at the expense of the Mining Institute, and the observations 
were taken by Captain Josiah Thomas, the manager of the mine. It is 
the deepest mine in Cornwall, and observations have been. taken at six 
points, at depths ranging from 252 to 2,124 feet. 
The deepest of these six observations was taken under very satis- 
factory conditions, being in clean granite, about 90 feet distant from any 
draught, and in newly-opened ground, only 24 feet from the end of the 
working. The temperature observed here—the thermometer having 
been left for some days in a hole bored for it—was 83° F., and the mean 
