Oct. 5, 1882] 



NATURE 



565 



apparatus, plugs for preventing convection-current in a bore or 

 well are referred to. Prof. Lebour's umbrella-like plug, in its 

 final form, appears to be very convenient, as it requires only one 

 wire. It remains collapsed so long as the wire is taut, but opens 

 out and pings the hole when it becomes slack. 



B. Methods of Observation. — These have chiefly been of 

 two kinds: 1. Observations in holes bored to the depth of a 

 few feet in newly-opened rock, either in the workings of a mine 

 or a tunnel, or in a shaft during the sinking. The rock should 

 not have been exposed for more than a week when the hole is 

 bored, and a day may be allowed to elapse for the heat generated 

 by boring to escape before the thermometer is inserted. Very 

 complete plugging is necessary to exclude the influence of the 

 external air. It is desirable to use about two feet of plugging, 

 of which the outer part should be made air-tight with plastic 

 clay or greased rag. After the lapse of a few days, the thermo- 

 meter is to be drawn out by means of a string attached to the 

 handle of its copper case, and the reading taken. The slow- 

 action thermometer above described is employed for this pur- 

 pose, and there is time to read it with sufficient deliberation 

 before any appreciable change occurs in its indication. It is 

 recommended that the thermometer be then reinserted and 

 plugged as before, and a second reading taken after the lapse of 

 a week. The majority of our successful observations have been 

 made by this method. 



2. Observations in deep bores of small diameter. The first 

 report contained a successful application of this method to 

 a bore about 350 feet deep, near Glasgow, which gave very 

 regular results in a series of observations at every sixtieth 

 foot of depth ; but in the majority of instances in which it has 

 since been applied, there have been marked irregularities, due 

 apparently to the influx of water from springs at particular 

 points. One of the most valuable of our results was obtained 

 hy the application of the method to a bore S63 feet deep, exe- 

 cuted at the bottom of a coal mine 1066 feet deep, giving a total 

 depth of 1929 feet. The bore in this case was dry at the time of 

 its execution, though full of water at the time of the observation. 

 It was in South Hetton Colliery, Durham. The instrument 

 generally employed in the observations of this class was a 

 maximum thermometer of either the Phillips or the Inverted 

 Negretti construction. 



The larger the diameter of the bore, the more uncertain does 

 this mode of observation become. The South Hetton bore had 

 a diameter of 2.\ inches. The Kentish Town well, 1000 feet 

 deep, in which Mr. Symons' observations were made, had a dia- 

 meter of 8 inches, and the well 660 metres deep at La Chapelle, 

 in the north of Pans, had a diameter of 44 feet (V., VI., VII.). 

 The temperatures in this last were proved to be largely affected 

 by convection, the water at the top being too warm, and that at 

 the bottom not warm enough. The ob-ervationsof Herr Dunker, 

 in the bore at Sperenberg, near Berlin, with a depth of 3390 

 feet and a diameter of 12 inches, proved a similar disturbance, 

 amounting at the top and bottom, to several degrees. As re- 

 gards the bottom, the proof consisted in showing that when a 

 thermometer at the bottom was protected by a tight plug from 

 the influence of the water above, its indications were higher by 

 3° R. (= 6}° F.) than when this precaution was not employed. 



C. Questions affecting the Correctness of' the 

 Observations made might theoretically include questions as 

 to the correct working of the instruments employed, and as to 

 the personal reliability of observers ; bat the latter topic has not 

 come into discussion, and the former has not ari>en since our 

 present patterns of instrument came into use. The questions for 

 discussion are thus ^confined to those which relate to possible 

 differences between the temperature of the point at which the 

 thermometer was placed and the normal temperature at the same 

 depth in its vicinity. 



1. The heat generated by the action of the boring tool will 

 vitiate the observation if sufficient time is not allowed for its 

 escape. 



A very full discussion of this subject in connection with the 

 great artesian well at La Chapelle will be found in reports V., 

 VI., and VII., clearly establishing the fact that the temperature 

 at the bottom both on the third and the sixth day after the ces- 

 sation of boring operations, was "]\" F. higher than after the 

 lapse of four months, though the water had been left to itself 

 during this interval. Further evidence showing that the tem- 

 perature in the lower part of a bore full of water may thus be 

 raised several degrees, is furnished by the Sub-Wealden bore. 



2. The generation of heat by local chemical action is well 



known to be a powerful disturbing cause when pyrites is present. 

 The observers in the mines of Schemnitz say, " Pyrites and also 

 decaying timber wer* 3 avoided, as being known to generate 

 heat." The observations in the coal mines of Anzin show a 

 temperature of 70^° F. in shaft IV. (a very dry one) at the depth 

 of 21 "2 metres, or less than 70 feet. This must be about 15' F. 

 above the normal temperature. In shaft II. the observer men- 

 tions that there was, at a depth of 90m., a seam of coal in which 

 heat was generated by oxidation. 



At Talargoch lead mine, in Flintshire, the discrepancies be- 

 tween the temperatures at the six observing stations are suggestive 

 of local chemical action. 



3. Convection of heat has proved a very troublesome disturbing 

 cause. 



As to convection of heat by air in a shaft or well not filled 

 with water, evidence will be found in the second report, both in 

 the case of Mr. Hunter's observations in the shafts of two salt 

 mines at Carrickfergus, having the depths of 570 and 770 feet 

 respectively, and in the case of Mr. Symons' observations at 

 Kentish Town, where the first 210 feet of the well are occupied 

 with air. At the depth of 150 feet the temperature was S2 - I in 

 January, and 547 in July. 



Convection of heat by water in old shafts which have been 

 allowed to become flooded, is very manifest in some of the ob- 

 servations communicated by Mr. Burns in the second and fourth 

 reports. In Allendale shaft (Northumberland), 300 feet deep, 

 with about 1 50 feet of water, the temperature was practically the 

 same at all depths in the water, and this was also the case in 

 Breckon Hill Shaft, where the observations extended from the 

 depth of 42 feet to that of 350 feet. A similar stale of things 

 was found in a shaft at Ashburton (Devon) by Mr. Amery, who 

 observed at every fiftieth foot of depth down to 350 feet. 



Convection by water in the great well at La Chapelle, 660 m. 

 (2165 feet) deep, and I '35 m. (4 feet 5 inches) in diameter at the 

 bottom, appears probable from the following comparisons : — 



Very concordant observations (communicated by M. Walferdin 

 to Comptts rendus for 1838) at three different wells in the Paris 

 basin of the respective depths of 263m., 400m., and 600m., 

 show by comparison with one another and with the constant 

 temperature in the artificial caves under the Paris Observatory a 

 rate of increase of 1° F. in 56 or 57 feet. These data would 

 give, at the depth of loom., or 328 feet, a temperature of 57 , 

 and at the depth of 660 m., or 2165 feet, a temperature of 90° ; 

 whereas the temperatures actually observed at those depths in 

 the well at La Chapelle in October, 1S73, when the water had 

 been undisturbed for a year and four months, were 59° 'J and 

 76°. It thus appears probable that the upper part of the well is 

 warmed, and the lower part cooled, by convection. Further 

 light may be expected to be thrown on this point when the well 

 reaches the springs, and the water spouts above the surface, as 

 it does at the Puits de Crenelle. A letter received by the 

 secretary in July, 1S82, states that engineering difficulties have 

 prevented any deepening of the well since the above observa- 

 tions, but that arrangements for this purpose have now been 

 made. 



More certain and precise information as to the effect of con- 

 vection in deep bores is furnished by the experiments of Herr 

 Dunker at Sperenberg. The principal bore at Sperenberg has 

 a depth of 4052 Rhenish, or 4172 English feet, and is entirely in 

 rock salt, with the exception of the first 283 feet. Observations 

 were first taken (with a maximum thermometer on the overflow 

 principle) at numerous depths, from 100 feet to the bottom, and 

 showed a fairly regular increase of temperature downwards. The 

 temperature at 700 feet was l6°'o8 R., and at 3390 feet 34°'! R. 

 Plugs were then contrived which could be fixed tight in the bore 

 at any depth with the thermometer between them, or could be 

 fixed above the thermometer for observing at the bottom. Con- 

 vectior was thus prevented, and a difference of one or two 

 degrees Reaumur was found in the temperatures at most of the 

 depths ; at 700 feet the temperature was now !7° - o6 R., and at 

 3390 feet 36°'IS. We have thus direct evidence that convection 

 had made the temperature at 3390 feet 2°05 R., or 4° - 6 F. too 

 low ; and this, as Herr Dunker remarks, is an under-estimate of 

 the error, inasmuch as convection had been exerting its equalising 

 action for a long time, and its effect could not be completely 

 destroyed in the comparatively short time that the plugs were in 

 position. Again, as regards the effect of convection on the 

 upper part of the bore, the temperature n°'o R was observed at 

 the depth of 100 feet in the principal bore when no plugs were 

 employed, while a second bore only ioa feet deep in its imme- 



