ON THE RATE OF INCREASE OF UNDERGROUND TEMPERATURE. 47 
temperature of the air in the district for the past thirty-five years is 
given by Dr. Hudson, of Redruth, as 51°°-4. Assuming 52°:5 as the mean 
temperature of the surface of the ground, we have an increase of 30°'5 in 
2,124) feet, which is at the rate of 1° F. in 70 feet. 
This determination seems to be worthy of all confidence. The other 
five observations were in places which had been for long periods exposed 
to the air. The six observations, in order of depth, are given in the 
following table. The last column shows the rate calculated by com- 
_ paring the depth in question with an assumed temperature of 52°-5 at 
the surface. 
Station | Depth in feet | Temp. Fahr. | eit PD se Bess Pen aaa 
| 
1. ey 64 115 22 
IL. | 390 | 65 1255 31 
III. | 876 | 67°8 153 57 
IV. | 1118 65 125 89 
Vv. | 1884 70 175 108 
VI. | 2124 83 30°5 70. 
Captain Thomas states that in the level where Station IV. was 
situated a cold current of air had been passing until quite recently ; also 
that the observation at Station V. is of little value, being made in a 
narrow portion of rock left between two lodes which had been worked away. 
All the obervations were taken in holes bored in the rock, not in the 
mineral veins. ‘Che rock is granite, except for the first 800 feet, which 
consist of a compact slate-rock called ‘killas,’ up to within 20 or 30 feet 
of the surface. There was a large quantity of pyrites in the upper 
workings, but the lode in these places was worked away seventy or 
eighty years ago. There is no pyrites in the deep workings, and no 
heating by chemical action has been noticed. The lode in the deepest 
part is chiefly composed of chlorite, quartz, and tin ores. All the holes 
in which observations were taken were dry. Water issues from the 
rock to the south of the lode at the bottom of the engine shaft (120 feet 
below the deepest of the six observations) at a temperature of about 90°. 
The mine has been worked for about 120 years, copper being obtained in 
the upper and tin in the lower portions. 
A second set of observations under the sea have been obtained by 
Professor Lebour; this time from North Seaton Colliery, a few miles 
distant from Newcastle. A slow-action thermometer was employed, in 
the usual manner, and six readings were taken, all showing the same 
temperature, 61°. The point of observation was half a mile beyond low- 
water mark, and 660 feet below mean sea-level (Ordnance datum). The 
depth of water, according to the Admiralty charts, is from 5 to 6 
fathoms, and as these charts give the depth of low water of spring tides, 
the depth at mean tide may be taken as about 40 feet. The point of 
observation is, therefore, 620 feet below the sea-bottom. Assuming the 
‘mean temperature of the sea-bottom to be 48°, we have an increase of 
15° in 620 feet, which is at the rate of 1° in 48 feet. 
Mr. EH. Garside has taken another observation in Ashton Moss 
Colliery, 90 feet deeper than before. He finds a temperature of 84° at 
the depth of 2,880 feet, whereas he previously found 85°'3 at the depth of 
2,790 feet. The thermometer used was the same, but it was left forty- 
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