710 



SCIENCE 



[N. S. Vol. XXVIII. No. 725 



tained at one locality with those obtained 

 at another is the safest procedure. "We 

 must accordingly wait for an increased 

 number of results before much can be in- 

 ferred. I will now lay the cases of the two 

 great tunnels as briefly as possible before 

 you. 



And first as to the temperature effects 

 observed in the two eases. 



The Simplon tunnel for a length of some 

 seven or eight kilometers lies at a mean dis- 

 tance of about 1,700 meters from the sur- 

 face. At the northerly end of this stretch 

 the rock temperature attains 55°, and at 

 the southern extremity has fallen to about 

 35°. The temperature of 55° is the 

 highest encountered. The maximum pre- 

 dicted by Stapff, basing his estimates on 

 his experience of the St. Gothard tunnel, 

 was 47°. Other authorities in every case 

 predicted considerably lower temperatures. 

 Stockalper, who also had experience of the 

 St. Gothard, predicted 36° at a depth of 

 2,050 meters from the surface, and Heim 

 38° to 39°.!^ 



When the unexpectedly high tempera- 

 tures were met with, various reasons were 

 assigned. Mr. Fox has suggested volcanic 

 heat. Others point to the arrangement of 

 the schistosity and the dryness of the rocks, 

 where the highest temperatures were read. 

 The latter is evidently to be regarded more 

 as explanation of the lower temperatures 

 at the south end of the tunnel, where the 

 water circulation was considerable, than of 

 the high temperatures of the northern end. 

 The schistosity may have some influence in 

 bringing the isogeotherms nearer to the 

 surface; however, not only are the rocks 

 intensely compact in every direction, but 

 what schistosity there is by no means in- 

 clines in the best directions for retention 

 of heat. From the sections the schistosity 



" See the account given by Schardt, Verhandl. 

 Schweiserischen Naturf. Gesellsch., 1904, 87, 

 " Jahresversammlung," pp. 204 fif. 



appears generally to point upwards at a 

 steep angle with the tunnel axis.^* 



Where there is such variability in the 

 temperatures, irrespective of the depth of 

 overlying rock, there is difficulty in assign- 

 ing any significant mean gradient. The 

 highest readings are obviously those least 

 affected by the remarkable water-circula- 

 tion of the Italian side. The higher 

 temperatures afford such gradients as 

 would be met in borings made on the level 

 — about 31 meters per degree. 



The temperatures read in the St. 

 Gothard rocks were of a most remarkable 

 character. For the central parts of the 

 tunnel the gradients come out as 46.6 

 meters per degree. Stapff, who made these 

 observations and conducted the geological 

 investigations, took particular pains to as- 

 certain the true surface temperatures of 

 the rock above the tunnel; and from these 

 ascertained temperatures, the temperatures 

 in the tunnel rock and the overlying height 

 of mountain, he calculated the gradients. 



But this low gradient is by no means the 

 mean gradient. At the north end, where 

 the tunnel passes through the granite of 

 the Finsteraarhorn massif, there is a rise 

 in the temperature of the rock sufficient to 

 steepen the gradient to 20.9 meters per 

 degree. Stapff regarded this local rise of 

 temperature as unaccountable save on the 

 view that the granite retained part of the 

 original heat. This matter I will presently 

 return to. 



Now, it is a fact that the radium-content 

 of the Simplon rocks, after some allowance 

 for what I have referred to as sporadic 

 radium, stands higher than is afforded by 

 the rocks in the central section of the St. 

 Gothard, where the gradient is low. For 

 the Simplon the general mean is (on my 

 experiments) 7.1 billionths of a gram per 

 gram. This mean is well distributed as 

 follows : 



" Schardt, loc. oit. 



