76 REPORT— 1882. 



inserted. Very complete plugging is necessary to exclude the influence 

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

 which the outer part should be made airtight with plastic clay or greased 

 rag. After the lapse of a few days, the tliermometer 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 purpose, and there is time to read it with suGBcient 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 

 by the application of the method to a bore 863 feet deep, executed at the 

 bottom of a coal mine 1,066 feet deep, giving a total depth of 1,929 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, 

 Dui-ham, and the observer was Mr. J. B. Atkinson (V., VI.). The instru- 

 ment generally employed in the observations of this class was a maximum 

 thermometer of either the Phillips or the Inverted Negretti construction, 

 as described above. 



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

 mode of observation become. The South Hetton bore had a diameter of 

 2h inches. The Kentish Town well, 1,000 feet deep, in which Mr. Symons' 

 observations were made, had a diameter of 8 inches (II., III., IV.), and 

 the well 660 metres deep at La Chapelle, in the north of Paris, had a 

 diameter of 4^ feet (V., VI., VII.). The temperatures in this last were 

 proved to be largely afiiected by convection, the water at the top being too 

 warm, and that at the bottom not warm enough. The observations of 

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

 3,390 feet and a diameter of 12 inches, proved a similar disturbance, 

 amounting at the top and especially at the bottom to several degrees. As 

 regards the bottom, the proof consisted in showing that when a ther- 

 mometer 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. 



3. Where a shaft contains only a few feet of water at the bottom, a 

 thermometer lowered to the bottom of this water may be assumed to give 

 pretty nearly the normal temperature of the soil at this depth, and a few 

 of our observations have been taken in this way. 'No observations of any 

 valne for our purpose can be made in the portion of a shaft or well occu- 

 pied by air, as the temperature of such air is largely influenced by that 

 of the air at the surface. This is clearly proved by Mr. Symons' observa- 

 tion in 200 feet of air at Kentish Town (II., III.). 



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 ; but 

 the latter topic has not come into discussion, and the former has not arisen 



