59Q 



NATURE 



[Oct. 12, 1882 



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

 fell during this interval from 58"-l to 57°x>, would seem to indi- 

 cate an elevation of i° due to the heat generated hy the boring 

 tool. An assumed surface temperature of 49° (only o°9 lower 

 than that of the Botanic Gardens in London) would give by 

 comparison v. ith 57°, at 1004 feet, a rate of 1° in 1 251 feet, and 

 by comparison with 59°, at 1302 feet, a rae of 1° in 130 feet, 

 which last may be adopted as the best determination. The 

 rock consists of the pebble beds of the Bunter or Lower Trias, 

 and the boring was executed at the rate of nearly ico feet per 

 month. v 



The boring at Swinderby, near Scarle (Lincoln), in search of 

 coal, was carried to a depth of 2000 feet, with a diameter at the 

 lower part of only 3J inches — a circumstance favourable to 

 accuracy, both as impeding convection and as promoting the 

 rapid escape of the heat of boring. The temperature at the 

 bottom was 79°, the water having been undisturbed for a month, 

 and this by comparison with an assumed surface temperature of 

 50 gives a rate of i° in 69 feet. 



The rocks are Lower Lias, New Red Marl (569 feet thick), 

 New Red Sandstone (790 feet thick), Red Marl, and earthy 

 Limestone 



The following results have been obtained from shallow 

 borings. The first three were made under Sir William Thom- 

 son's direction, with a thermometer which could be read by 

 estimation to hundredths of a degree :— 



Blythswood bore, near Glasgow, with a depth of 347 feet, 

 gave a very regular increase of i° in 50 feet. 



Kirkland Neuk bore, in the immediate vicinity of the above, 

 gave consistent observations at different seasons of the year from 

 180 feet to the bottom (354 feet), the rate being i° in 53 feet. 

 This bore passed through coal which had been "very much 

 burned or charred." 



South Balgray bore, near Glasgow, and north of the Clyde, 

 with an available depth of 525 feet, gave by comparing the 

 temperature at the bottom with that at 60 feet a rate of 1° 

 in 41 feet. 



Shale extends continuously from 390 to 450 feet from the 

 surface, and the increase in these 60 feet of shale was 2°02, 

 which is at the rate of 1° in 30 feet. This rapid increase agrees 

 with the fact that shale has very low conductivity, averaging 

 •0019 in Trof. Herschel's experiments. 



The only small bore remaining to be mentioned is that at 

 Manegaon, in India, which had 310 feet available, and gave by 

 comparing the temperature at this depth witli that at 60 feet a 

 rate of 1° in 68 feet. The rocks consist of fine softish sand- 

 stones and hard silty clays, the dip being 10°. 



4. Tunnels.— The Mont Cenis tunnel, which is about seven 

 miles long, is at a depth of exactly a mile (5280 feet) be- 

 neath the crest of Mont Frejus overhead. This was the 

 warmest part of the tunnel, and had a temperature of 85°-! F. 

 The mean air temperature at the crest overhead was calculated 

 by the engineer of the tunnel, M. Giordano, by interpolating 

 between the known temperature of the hill of San Theo- 

 dale and that of the city of Turin, the former being 430 metres 

 higher, and the latter 2650 metres lower, than the point in 

 question. It is thus calculated to be - 2°'6 C. or 27° # 3 F. If, 

 according to our usual rule, we assume the ground to be 1° 

 warmer than the air, we have 28° 3 to compare with 8s°-l. This 

 gives a rate of 1° in 93 feet ; but, inasmuch as the convexity of 

 the surface increases the distance between the isotherms, a cor- 

 rection will be necessary before we can fairly compare this result 

 with rates under level ground. As a rough estimate we may 

 take \ of 93, and adopt i° in 79 feet, as the corrected result. 



' The rocks on which the observations have been made are 

 absolutely the same, geologically and otherwise, from the 

 entrance to the tunnel, on the Italian side, for a dislance of 

 nearly 10,000 yards. They are not faulted to any extent, though 

 highly inclined, contorted, and subjected to slight slips and 

 slides. They consist, to a very large extent indeed, of silicates, 

 chiefly of alumina, and the small quantity of lime they contain is 

 a crystalline carbonate." 



The St. Gothard Tunnel, v, hich has a length of about nine 

 miles, has been subjected to much more minute observation, a 

 skilled geologist, Dr. Stapff, having, under Government direc- 

 ti .11, devoted bis whole time to investigating its geology and 

 physics. He not only observed the temperature of the rock in 

 the tunnel at very numerous points, but also determined, by 

 observations of springs, the mean temperatures of the surface of 

 the mountain at various points, and compared these with an 



empirical formula for air temperature deduced from the known 

 mean temperatures of the air at Goschenen, Andermatt, Airolo, 

 and the Hospice of St. Bernard. He infers from his com- 

 parisons a considerable excess of soil above air temperature, 

 increasing from 2° C. at the ends of the tunnel to 6° C. at the 

 crest of the mountain over the centre of the tunnel. The highest 

 temperature of the rocks in the tunnel was at this cen'ral part, 

 and was about 30°-6 C. or 87° F. The soil temperature at the 

 crest above it was about - o°'6 C.,-or 31° F., giving a differ- 

 ence of 56° F. The height of the crest above sea-level was 

 about 2S50 m., and that of the tunnel at this part 1150 m., 

 giving a difference of 1700 m. or 5578 feet. The rate of in- 

 crease here is, therefore, about 1° F. in 100 feet ; and if we 

 apply the same correction for convexity as in the case of the 

 Mont Cenis Tunnel, this will be reduced to about 1" F. in 87 

 feet, as the equivalen rate under a level surface. From com- 

 bining his observations in all parts of the tunnel through the 

 medium of empirical formula?, Dr. StapfT deduces an average 

 rate of 1° F. for every 88 feet measured from the surface directly 

 overhead. Where the surface is a steep ridge, the increase was 

 less rapid than this average ; where the surface was a valley or 

 plain, the increase w.is more rapid. As this average merely 

 applies to the actual temperatures, the application of a correc- 

 tion for the general convexity of the surface would give a more 

 rapid rate. If we bring the isotherms nearer by one part in 15, 

 which seems a fair assumption, we shall obtain a rate of 1° F. in 

 82 feet. 



Collecting together all the results which appear reliable, and 

 arranging them mainly in the order of their rates of increase, 

 but also with some reference to locality, we have the following 

 list :— 



Bootle waterworks (Liverpool 



Przibram mines (B ihemia) 



St. Gothard tunnel 



Mont Cenis tunnel 



Talargoch le.id mine (Flint) 



Nook Pit, Colliery 

 Bredbury ,, ... I East 



Ashton Mo-s ,, ... I Manchester 



I'e iton „ .. I coalfield. 



Astley Pit, Dukinfield I 



Schemnitz mines (Hungary) 



Scarle boring (Lincoln) 



Manegaon boring (India) 



Pontypridd cilliery (S. Wales) 



Kingswood colliery (Bristol) 



Radstock ,, (Bath) 



Paris artesian well, Crenelle 



i, „ St. Andre 



i> ,i Military School 



London „ Kentish Town ... 



Rosebridge colliery (Wigan) 



Vakoutsk, frozen ground (Siberia) ... 

 Sperenberg, boring in salt (Berlin) ... 



Seraing collieries (Belgium) 



Monkwearmouth collieries (Durham) 

 South Hetton ,, „ 



Boldon ,, ,, 



Whitehaven ,, (Cumberland) 



Kirkland Neuk bore (Glasgow) 

 Blythswood ,, ,, 



South Balgray ,, „ 



Anzin collieries (North of France) 

 St. Petersburg, well (Russia) ... 

 Carrickfergus, shait of salt mine (Ireland) 



Slitt mine, Weardale (Northumberland) 



The depth stated is in each case that of the deepest observation 

 that has been utilised. 



F. In deducing a Mean from these very Various Re- 

 sults, it is better to operate not upon the number of feet per de- 

 gree, but upon its reciprocal — the increase of temperature per foot. 

 Assigning to the results in the foregoing list weights proportional 

 to the depths, the mean increase of temperature per foot is found 

 to be '01563, or about „\ of a degree per foot— that 1 . 1 I . 

 in 64 feet. 



It would be more just to assign greater weight to tho' r e single 

 results which re] -resent a large district or an extensive group of 



