Scpi. 9, i8So] 



NATURE 



443 



faults which throw down coal-measure shale ; and as the faults have 

 a considerable inclination, the lowest workings run beneath the 

 shale for a considerable distance. The limestone dips at angles 

 varying from 45° to 55°, and is of two kind?, one white and 

 massive, the other thin bedded black with thin shale partings. 



There are levels at intervals of about twenty yards vertically, 

 in the vein, most of \\ hich have been driven for some years ; but 

 all the observations have been taken in newly-opened ground. 



They have been taken by boring a hole 24 inches deep at a 

 distance of from li to 5 yards from the fore breast, and either on 

 the same day or on the next day inserting one of the Committee's 

 slow-action thermometers, with a foot of plugging consisting of 

 dry rag and clay behind it. After an interval generally of four 

 •days the thermometer was taken out and read, then reinserted, 

 and read again about a week later, the difference between the 

 two readings never amounting to so much as half a degi'ee. 



The observations were taken at six different places in the 

 mine, which are deiignated by the observers Stations I. to VI. ; 

 but in one instance, that of Station II., owing to the swelling of 

 mewly-exposed shale, the hole became distorted, so that after 

 extracting the dry rag and clay, an hour was expended in work- 

 ing out the thermometer, the reading of which has therefore 

 been rejected. The following is a list of thefive remaining 

 stations, arranged in order of depth : — 



No. of 

 Station. 



IV. 

 V. 

 VI. 



III. 

 I. 



Distance and 



Most>-n Shaft. 

 I go yds. S.W. 

 170 yds. S.E. 

 840 yds. S.W. 

 120 yds. S. 

 190 yds. N.E. 



It will be observed that the order of the temperatures is not 

 the same as the order of the depths ; it therefore becomes im- 

 ■portant to describe the positions with some particularity. 



Stations IV., V., and III. are near together in ground plan, 

 IV. and V. being about 250 yards apart, and III. nearly mid- 

 way between them, and they have all the same rock overhead 

 between them and the surface, namely, black and white lime- 

 stone. 



At Station I. the rock overhead consists almost entirely of 

 sandstones and shales, with thin coal-seams. At Station VI. it 

 ■consists of white limestone and shale. 



It may be mentioned that the temperature at VI. was observed 

 on three several occasions, namely, January 14, January 21, and 

 February ig, and was in each case found to be the same. Mr. 

 Strahan further states that this station is near a large fault, 

 which contains iron pyrites and gives off water charged with 

 snlphuretted hydrogen ; the temperature of the water as pumped 

 •up Walker's shaft from a depth of 770 feet, being 63° at the 

 topof the lift. It seems probable that the decomposition of this 

 pyrites may be the cause of the exceptionally high temperature 

 at this station. 



• The comparison of the temperatures will be most clearly 

 brought out by tabulating the rate of increase from the surface 

 down to each station, as calculated from an assumed surface 

 temperature, which may be fairly taken as 48°. As all the 

 depths are considerable, an error of a degree in the surface 

 temperature will not have much influence on the com; arison, 

 which stands thus : — 



Depth Excess above Feet per 



Station. in feet. surface. Degree. 



IV. ... 465 .- 5°-4 .- 86 



V. ... 555 •■• 49 •■• 113 



VI. ... 636 ... lo-S ... 59 



III. ... 660 ... 6-0 ... no 



I. ... 1,041 ... I2-S ... 81 



Stations V. and III., which give the slowest rate of increase, 

 are both of them in a vein called the " South Joint ; " and 

 Stations IV. and I., which agree well with each other, though 

 •differing from the rest, are both of them in another vein 

 •called the "Talargrch vein;" while Station VJ. is in the 

 " Country rock." The horizontal distance between IV. and III. 

 is only 120 yards; but if we attempt to deduce the rate of 

 •increase from comparing these two, n e have an increase of only 

 •o-°6 in 195 feet. It thus appears that, notwithstanding the 

 piroximity of the two veins, their conditions as to temperature 

 are very different. 



Widely as the results differ among themselves, they agree upon 



the whole in showing that the average rate of increase is slow ; 

 and this general result is in harmony with what has been found 

 at the nearest localities mentioned, in our previous report, 

 namely, Dulinfield and Liverpool. Here, as at Dukiufield, all 

 the strata are highly inclined. 



Some additional observations at Dukinfield have recently been 

 made for the Committee by Mr. Edward Garside, student of 

 engineering in Queen's College, Belfast. The Astley Pit, in 

 which they were taken, has now been carried to a much greater 

 depth than it had extended at the time of Sir Wm. Fairbairn's 

 observations, to which allusion was made in our Report for 

 1870. The two deepest seams of coal in it are called the 

 " Cannel Mine" and the "Black Mine," the former being the 

 deeper of the two ; they both slope downwards at about 15", the 

 deepest point being the far end of the Cannel Mine. The 

 following is Mr. Garside's summary of the observations ; the 

 "surface-depth" being distinguished from the "shaft-depth," 

 because the surface is not level, but slopes slightly in tlie same 

 general direction as the seams. The shrft-depth gives the 

 difference of levels, but the surface-depth, which is practically 

 the same as the distance of the nearest point of the surface, 

 is what we must use in computing the rate of increase ot 

 temperature. 



Surface 

 Dept!i. 



Shaft 

 Depth. 



Feet. Feet. ] Fahr. Fahr. Yards. 



June 17 Cannel 2,700 2,754 86J 75* 160 



,, ig Black 2,407?,- 2,631 So" 78I 630 



,, 21 Cannel 2,4l6i 2,482 J 81 79 600 



July 2 Black i,g87| 2,047! 74 71^ 460 



The pit is described as beijg entirely free from water. 



Report of the Commiitt'c for makitig Secular Rxferiments on 

 the Elasticity of Wires, by Mr. J. J. Bottomley. — The wires pre- 

 pared by the Committee in Glasgow are still under experiment. 



Report of the Committee on the Speeife Inductive Capacity of a 

 good Spren^el Vacuum, by Mr. W. E. Ayrton. — Boltzmann had 

 estimated the specific inductive capacity at ■g994 ; while Pro- 

 fessors Ayrton and Perry had estimated it at '9985. In the 

 experiments of the committee much higher vacua had been 

 obtained, and had found some rather remarkable and not readily 

 intelligible results. With very high vacua the inductive capacity 

 of the compound aluminium condenser employed appeared to be 

 less than at slightly lower degrees of exhaustion. The method 

 adopted consisted in applying the aluminium condenser to a 

 modification of a Hughes' induction balance in connection with 

 a sliding condenser, a telephone, and a small induction coil. 



Sir W. Thomson criticised the method as not being purely 

 electrostatic in its nature. The discussion was continued by Mr. 

 Gordon and Mr. Fitzgerald, who alluded to a possible connec- 

 tion between the fluctuations of the phenomena observed and 

 those observed in the phenomena of Crookes' radiometer-force. 



All the observations w-ere taken with one cf the committee's 

 slow-acting thermometers, in holes drilled in the floors at the far 

 ends of newly-opened horse-road levels ; the holes being four 

 feet deep and two inches in diamettr. All the holes were free 

 from cracks, and were in the same kind of rock — an argillaceous 

 earth called "warren earth." They were allowed to stand for a 

 short time, to allow the heat caused by drilling to escape. The 

 thermometer was then inserted, and the portion of the hole 

 between it and the mouth plugged w ith cotton waste and the dust 

 which came out of the hole in drilling. After being left for 

 forty-eight hours it was taken out and read. 



The data for calculating the rate of increase are given in the 

 first two columns below. 



Depth Temperature Feet per Deeree 



in Feet. Fahr. from Surface. 



i,987i 74 79-5 



2,4t6i 81 75-5 



2,407i So 777 



2,700 S6.5 72 



The third column shows the number of feet per degree of 

 difference from the surface, assuming the surface-temperature to 

 be 49". 



Comparing the observations at 1,987^ and 2,416^ feet, we 

 have an increase of 7" in 429 feet, which is at the rate of 1° in 

 61 "3 feet; and comparing the two deepest observation.s, ve 

 have an increase of 6^' in 292! feet, which is at the rate of 1° in 



