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value. It was also suggested that the mean temperature of the surface overhead should be examined by boring.

M. Sismonda speedily replied, stating that he fully recognized the importance of such experiments, and had already made arrangements with the Government at Turin, and with the contractors for the railway works, to have them carried out as fully and fairly as possible. Had the communication reached him at a time of year when he could have travelled without great inconvenience, he would have gone to the spot himself; but as that was now impossible, the Government Commissioner for the works, M. Salvatori, had undertaken to see the experiments carried through by employés under his orders. M. Sismonda further stated that, from the commencement of the tunnel, the Academy of Sciences of Turin had instituted a series of scientific observations in it, in which observations of temperature were included. The results of these observations he promised to forward as soon as they were completed and tabulated.

On the receipt of the final refusal to bore down at the bottom of Rosebridge Colliery, inquiries were instituted as to the feasibility of executing a similar operation in the deepest part of the Alpine tunnel. The contractors hare, however, declined to grant permission, as the operation would involve additional encumbrance of the very narrow space in which their works are proceeding. It appears that a length of a mile or more in the deepest part of the tunnel has not yet been opened out to the full width, so that opportunity may yet be given to excavate a lateral heading and bore down, if the Association encourage the plan.

Mr. G. J. Symons has repeated his observations in the Kentish Town well, at every fiftieth foot of depth, from 350 to 1100 feet, which is the lowest point attainable. As the water begins at the depth of 210 feet, all these observations may be regarded as unaffected by the influence of the external air, and they have now been sufficiently numerous at each depth to render further verification needless. The following are the results finally adopted, and they do not differ materially from those first published (Report for 1869).

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The numbers in the last column are the quotients of those in the two preceding, and denote the average number of feet of descent for 1° F. of increaso, as deduced from comparing the temperature at each depth of observation with the temperature at the lowest depth. The earlier numbers in this column of course carry more weight than the later ones. The amount of steadiness in the increase of temperature of the water is best seen by inspecting the third column, which shows that the freest interchange of heat occurs at about the depth of 600 feet. This must be due to springs. The soil, from the depth of 569 to that of 702 feet, is described as light-grey chalk, with a few thin beds of chalk-marl subordinate.” The soil consists in general of chalk and marl, from 325 to 910 feet, and below this of sandy marl, sand, and clay (see list of strata in last year's Report, p. 41). The mean rate of increase in the former is a degree in 56 feet, and in the latter a degree in 49 feet. The mean rate of increase from the surface of the ground to the lowest depth reached is certainly very nearly 1° F. in 54 feet.

Mr. David Burns, of H.M. Geological Survey, has furnished observations taken in the W. B. lead-mines, at and near Allenheads, Northumberland, by the kind permission of Thomas Sopwith, Esq., F.R.S., and with the valuable assistance of Mr. Ridley, Underground Surveyor, who continued the observations after Mr. Burns had left.

The mineral for which these mines are worked is galena. There are very extensive old workings at a lower level than the present workings, and filled with water, which is kept down by pumping; but the quantity daily pumped out is very small in comparison with the whole, so that the change of water is slow.

From the offices of the lead-mines a small windlass with a supply of fine brass wire was obtained, which enabled the thermometer to be lowered steadily and quickly.

The first observations were taken in Gin-Hill shaft, 3rd June, 1871. The observers proceeded as far down in the works as they were able, and took their station in a level leading from the shaft, 290 feet from the surface of the ground, and 38 feet above the surface of the water in the shaft. The following observations were then made :Depth under

Depth in

Temperature.
ground.
water.

Fabr.
ft.

ft. 340

12

49.3 340

12

49.2 390

62

51.2 390

62

51.2
440
112

51.3
440
112

51-3

The mean temperature at the shaft mouth for the year ending 31st May 1871, was 44°3, as derived from daily observations of maximum and minimum thermometers, without applying a correction for diurnal range. Adding 1° to this, to obtain the probable mean temperature of the surface of the ground, and taking the temperature at 400 feet of depth as 51'3, Mr. Burns computes that the rate of increase downwards is 6° in 400 feet, or 1° in 66.6 feet. The data for this calculation are obviously in many respects very uncertain.

On the 21st June Mr. Ridley took observations in another shaft in the same workings, called the High Underground Engine Shaft. It is sunk

water.

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65.4

from a level at the depth of 398 feet below ground, and the surface of the water in it is 399 feet down the shaft, or 797 feet below the surface of the ground. There are pumps in the shaft, but they had been stationary for more than 24 hours before the observations were made. Immediately after the observations they were started, and when they had been working for some time the temperature of the water lifted was found to be 650.2. They draw their water at a depth of 957 feet below the surface of the ground. The following were the observations:Depth under

Depth in

Temperature. ground.

Fabr. ft.

ft. 807

10 807

10

64.9 857

60
857
60

65.75
807
10

65.4 The thermometer could not be lowered beyond 857 feet without risk of losing it, by getting fast in the wooden framework with which the pumps were secured. Mr. Burns thinks that some of the temperatures here recorded are too low, from the index being shaken down by reason of the impediments presented by the upper portions of the framework. The surface of the ground over this shaft is about 300 feet higher than over Gin-Hill shaft. If we allow 1° for this increase of height, and call the temperature of the surface of the ground 44°3, as against 45°:3 at Gin Hill, we have, by comparison with the observed temperature 650.7 at the depth of 857 feet, an increase of 21°•4 in 857 feet, or 1° in 40 feet.

On the 6th July Mr. Ridley took observations in another sump or underground shaft at Slitt mine, Weardale. This shaft is sunk from the lowest level in the working, and had been standing full of water during the five months which had elapsed since it was sunk. The only source of disturbance was a little water running along the level across the top of the shaft, so as to enter the shaft (so to speak) on one side and leave it on the other.

This may affect the temperature at 3 feet, but could scarcely affect the temperature at 53 feet, which may be regarded as very reliable. The following are the observations :Depth under

Depth in

Temperature.
ground.
water.

Fahr.
ft.

ft. 610

3 610

3

64.5
660
53

65.1
660
53

64.9 Mr. Burns says “ the surface-temperature at Slitt mine will be nearly the same as that at Gin-Hill shaft, judging from their relative elevations, aspects, and exposure to the winds.” Assuming at then to be 45°3, and reckoning the temperature at 660 feet as 65°, we have an increase downwards of 199.7 in 660 feet, or 1° in 33.5 feet. The only datum that seems doubtful here is the surface-temperature. If, instead of 45°.3, it be assumed

44 as

Mr. Ridley has also taken observations in Breckon-Hill shaft, which is near the river Allen, about 1} mile from Gin-Hill shaft, and at an elevation

64.51

{*** 3}, it gives an increase of 1° in {*}3}feet

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46-7

not much above the bottom of the valley, but 1174 feet above sea-level. It was sunk some years ago, and has since stood nearly full of water. At the time of the observations the surface of the water was 24 feet down the shaft. The following are the observations taken in this shaft on June 13th:Depth under

Depth in

Temperature.
ground.
water.

Fahr.
ft.

ft.
50
26

47.2
50
26

47.2
100

76

46.9 100

76

46.85
150
126

46.8
150

126
200
176

46.6
250
226

46.8
300
276

46.8
350
326

46.9 These observations were taken early in the morning, when the air and springs were so cold as to allow the maximum thermometer to be cooled below the temperature of the shaft. In order to test more thoroughly the apparent uniformity of temperature from 100 feet down to 350 feet, Mr. Ridley took a second series of observations, extending from the 22nd to the 27th June. In these observations the thermometer was lowered in a tin case filled with water colder than that of the shaft. The thermometer was supported within the case in a vertical position by a wooden frame, and prevented from shaking about.

It was allowed to remain at each depth several hours, was then lifted, and read with all possible care. The following are the observations thus obtained :Depth under

Length of Temperature before Temperature after ground. immersion. immersion.

immersion. ft.

h
42
10 40

46 5
92
11 20

44:0

46.5
142
11 40

42:4

46.6
192
12 20

46.1

46.6
242
34 0

44:0

46.6
292
13 40

45.4

46.6
342
10 25

45.4

46.6 Here the temperatare is even more uniform than in the first series. As to the causes of this 'uniformity, Mr. Burns' remarks that the shaft is not connected with any working, but is cut through solid strata. few yards to the east of the Allen, while, in the bed of that stream, and making a great spread on the west side of the valley, is a bed of limestone nearly 70 feet thick, and dipping at an angle of about 10° to the east. The top of this limestone was cut in the shaft about 40 feet down, which occasioned a great influx of water into the shaft, and drained a strong spring on the other side of the river.

It will be observed that the chief difference between the two sets of observations is just at the place where this limestone was cut. The second set were taken after and during much rain, and the first set after a week of very little rain. It appears probable that the difference of temperature at this

m

42.0

It is a

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depth was due to the difference of temperature of the surface-water which soaked in through the limestone in the two cases. As regards the temperatures at depths exceeding 200 feet, it would appear that, in times of comparative drought (as in the first set), the heat of the soil at the greater depths has time to produce a little augmentation in the temperature of the water before it soaks away.

This shaft is obviously not adapted for giving any information as to the rate of increase downwards. Collecting the best determinations from the other shafts we have :

Depth of
Temperature.

Calculated thermometer.

Fahr.

increase. ft.

ft. Gin-Hill Shaft ....

400
513

i in 66-6 High Underground Engine 857

65.7

1 in 40 Slitt Mine

660
65.1

1 in 33.5 Mr. Burns considers that little or no weight should be attached to the first of these determinations, as a pumping-engine was working in a neighbouring shaft communicating with it at the time when the observations were taken. The jump of 2° in descending from 340 to 390 feet also renders the interpretation of these observations difficult.

The closeness of the temperatures in the other two shafts, at depths differing by about 200 feet, suggests the idea that they are both fed by the same spring, and that the temperatures indicated are the temperature of the origin of the spring slightly modified by the different temperatures of the strata through which it has passed; but their positions appear to render this impossible.

Mr. Burns's opinion from all the observations is that the mean rate of increase downwards at Allenheads is about 1° in 35 feet ; but this cannot at present be held as proved.

The strata consist mainly of alternate beds of sandstone and shale, with a few beds of limestone intermixed. In Slitt mine there is also a bed of basalt 158 feet thick, overlying the vein of fluor-spar in which the workings are carried on, the workings being 55 feet down in this vein.

Preparations are being made for taking observations in the dry part of the mines, by making shallow bores at different levels, inserting the thermometer, plugging up the hole for a few days, and then reading.

Another gentleman connected with H.M. Geological Survey, Mr. R. L. Jack, has taken observations in a bore at Crawriggs, Kirkintilloch, near Glasgow. They were taken on the 29th November 1870, the temperature of the air being 34o. The surface of the water in the bore was 6 feet below the surface of the ground, the latter being 200 feet above sea-level. The following were the observations :Depth from surface Time of lowering Time of withdrawing Temperature. of ground. thermometer. thermometer.

Fahr.
feet.
50
12 52 P.M.
1 7 P.x.

47
100
1 10
1 28

481
150
1 33
1 52

49
200
1 58
2 14

50
250
2 22
2 43

50
300
3 15
3 34

504
350
3 40
3 50

51 A few feet below 350 feet an obstruction in the bore prevented further

h m

h m

9

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