ON THE RATE OF INCREASE OF UNDERGROUND TEMPERATURE. 41 



At the Italian end, the temperatures 



28-2 287 29-5 



were found in the rock, at the distances from south portal 



4830 5101 5721 



and at the depths below surface vertically overhead 



1407 1513 ' 1252 



In English measures, these data are as follows : — 

 Temperatures (Fahrenheit) at Swiss end 



77°-9 79°-9 82°-0 82°-2 83°-8 



Distances from north portal (in miles) 



3-21 339 348 356 391 



Distances below surface (in feet) 



3100 3186 3225 3320 4101 



Temperatures (Fahrenheit) at Italian end 



82°-8 83°7 85°-l 



Distances from south portal (in miles) 



3-00 3-17 3-56 



Distances below surface (in feet) 



4615 4965 4108 



The mean rate of increase downwards in the whole length of the 

 tunnel is '02068 of a degree Centigrade per metre of depth, measured 

 from the surface directly over. This is 1°F. for 88 feet. Where the sur- 

 face is a steep ridge, the increase is less rapid than this average ; where 

 the surface is a valley or plain, the increase is more rapid. 



The boring in connection with the Liverpool "Waterworks at Bootle, 

 which was described in last year's Report as having attained a depth of. 

 1004 feet with a temperature of 58T, was completed in December, the 

 depth being 1302 feet, and the temperature at the bottom 59 - 0. The 

 boring ceased for six weeks at the depth of 1004 feet, and the temperature 

 fell during this interval from 58T to 57'0. The slowness of the increase 

 downwards, and the lowness of the temperature at the bottom, are very 

 remarkable. Mr. Symons found a temperature of 70 at the depth of 

 only 1100 feet in the Kentish Town Well, near London ; and Mr. Atkinson 

 found a temperature of 70 at 1366 feet in the boring at South Hetton 

 Colliery, Durham. A comparison of the temperature 59"0 at 1302 feet 

 at Bootle with the temperature 52 - at 226 feet gives an increase of only 

 7° in 1076 feet, or 1° for 154 feet. 



Mr. E. Wethered, F.G.S., F.C.S., has taken during the past year a 

 valuable series of observations at the Kingswood Collieries, near Bristol. 

 The instrument employed was one of the Committee's slow-acting 

 thermometers, which was inserted in holes two feet deep, bored in newly 

 exposed coal or rock, special care being taken to avoid currents of air. 

 As there is no explosive gas in these collieries, powerful ventilation is not 

 necessary ; and the headings in which the observations were made were 

 ventilated by means of a square wooden pipe (called a trunk) lying on 

 the floor, and serving for the exit of the air, while the entering air flows 

 above and beside it. This trunk was always drawn some distance back 

 from the end of the heading where the thermometer was inserted. 



As soon as the hole for the thermometer had been bored, it was closed 

 with clay rolled in the form of a plug, 6 inches long with a head, and the 

 thermometer was inserted about an hour afterwards, the mouth being 

 again closed as before. The holes were in most cases dry. 



The strata in which the observations were taken belong to the lowest 



