1871.] Mr. D. T. Ansted on the Earth's interior Temperature. 481 



May 25, 1871. 



General Sir EDWARD SABINE, K.C.B., President, in the Chair. 



Pursuant to notice given at the last Meeting, Capt. Douglas Galton 

 proposed and Prof. Huxley seconded the Right Hon. Robert Lowe, M.P., 

 for election and immediate ballot. 



The ballot having been taken, Mr. Lowe was declared duly elected. 



The following communications were read : — 



I. " On the Temperature of the Interior of the Earth, as indicated 

 by Observations made during the Construction of the Great 

 Tunnel through the Alps." By D. T. Ansted, M.A., F.R.S., 

 For. Sec. G.S. Received April 6, 1871. 



It had been arranged from the commencement of the Alpine tunnel 

 (often, though incorrectly, called the Mont-Cenis tunnel) that observations 

 should be taken at intervals of about one kilometre (3281 feet) from both 

 the French and Italian ends, with a view to determine as nearly as possible 

 the law of increment; and before the completion of the work it had become 

 evident that the ordinary estimate of increased temperature due to the depth 

 below the surface of the earth would by no means apply to this particular 

 case. The actual length of the tunnel being 40,140 feet, and the culmi- 

 nating point of the mountain being 5280 feet vertically above a point 

 21,156 feet from the Italian end, there was evidently scope for a number of 

 valuable observations. The result also might be expected to show the influ- 

 ence of marked irregularities in the contour of the mountains, and also of 

 changes in the nature of the rock. The experiments and observations 

 were entrusted to the resident engineers at each end of the tunnel, Signor 

 Borelli undertaking them from the Italian side. It does not appear that 

 any special construction of thermometer was supplied, or that the subject 

 greatly interested the resident engineers. Careful observations were made 

 and duly recorded by Signor Borelli, but the attempt failed in the hands of 

 his colleague at the other end. Thus one great source of value was lost, 

 and the observations at equal distances from both ends cannot be compared. 



The rocks through which the tunnel has been driven consist to a very 

 large extent of a peculiar calcareous schist, partly talcose, and containing 

 many bands and strings of quartz. The whole of the Italian end is through 

 rock of this kind, and it was reached at about 1 1,000 feet from the entrance 

 from the French side. The rocks on the French side were at first very 

 different, including nearly 7000 feet of a peculiar sandstone with indica- 

 tions of anthracite, about 1000 feet of very hard quartzite, and 3000 feet of 

 gypsum, limestone, and calcareous schist, a large proportion being gypsum. 

 It would have been in the highest degree desirable to have been able to 

 compare observations of temperature made at similar depths in different 



voi/. xix. 2 o. 



