512 REPORT—1868. 
The only observations yet taken in answer to the above invitation were 
made near Glasgow by Sir W. Thomson, from whose recent paper on Geo- 
logical Time (Trans. Geol. Soc. Glasgow, vol. ii. part 1) the following para- 
graph (§ 29) may now be quoted. 
«« All sound naturalists agree that we cannot derive accurate knowledge of 
underground temperature from mines. But every bore that is made for the 
purpose of testing minerals gives an opportunity of observation. If a bore 
is made, and is left for two or three days, it will take the temperature of the 
surrounding strata. Let down a thermometer into it, take proper means for 
ascertaining its indications, draw it up, and you have the measure of the 
temperature at each depth. There are most abundant opportunities for geo- 
thermic surveys in this locality, by the numerous bores made with a view 
to testing minerals, and which have been left, either for a time or perma- 
nently, without being made the centre of a shaft. Through the kindness of 
Mr. Campbell, of Blythswood, several bores in the neighbourhood of his 
house have been put at the disposal of the Committee of the British Associa- 
tion, to which I have referred. In one of these bores very accurate observa- 
tions have been made, showing an increase of temperature downwards, but 
which is not exactly the same in all the strata, the difference being no doubt 
due to different thermal conductivities of their different substances. I need 
not specify minutely the numbers ; but I may say, in a general way, that the 
average increase is almost exactly 1, of a degree Fahrenheit per foot of 
descent; which agrees with the estimate generally admitted as a rough 
average for the rate of increase of underground temperature in other lo- 
calities. 
«Another bore has been put at the disposal of the Committee, and the 
investigation of it is to be commenced immediately, so that [ hope in the 
course of a few days some accurate results will be got. It has been selected 
because the mining engineer states in his report that the coal has been very 
much burned or charred, showing the effect of heat ; and it becomes an in- 
teresting question, Are there any remains of that heat that charred the coal 
in ancient times, or has it passed off so long ago that the strata are now not 
sensibly warmer on account of it?” 
The following report of these observations has been sent by Sir W. Thomson 
to the Secretary of the Committee :— 
The operations were commenced in December last, with a spirit thermo- 
meter by Casella, having a stem 14 in. long, divided to tenths of a degree, 
and ranging from 39° to 61° Fahr.; it has a bulb 33 in. long by 1 in. diameter, 
is enclosed in an outer tube, nearly filled with spirit, and hermetically 
sealed; a protecting case of strong tin covered the whole; and to this case a 
stout copper wire was attached for lowering it in the bore. 
Before commencing the operations, the thermometer, thus mounted, was 
left in a vessel of water until the temperature remained unchanged ; it 
was then plunged into another vessel whose temperature differed by about 
10° Fahr. from the former, and an interval of more than a minute elapsed 
before any change of reading could be observed ; it was also ascertained that 
it could be raised from a depth of 60 fathoms and a reading taken within 
this time. The following observations were then made at Blythswood, 
about five miles west of Glasgow, during December and January, in a bore 
(No. 1) 60 fathoms deep, and filled with water to a constant depth of about 
2 fathoms from the surface :— 
