Radium Content of Rocks of the Loetschbert/ Tunnel. 467 



kept, as it has been Pound that any strong light affects the 

 insulating powers of the sulphur support ot" the gold leaf. 

 It was found by taking these precautions that the natural 

 leak of the electroscope remained fairly constant at about 

 six scale divisions per hour, but this leak was, however, 

 determined for each experiment separately. 



The Loetschberg tunnel runs from Ivandersteg to Goppen- 

 stein in the Bernese Oberland. As originally planned, the 

 tunnel was to be straight and .13,744 m. in length, but 

 owing to an incursion of water while passing under the 

 Kander River, it was found necessary to deviate from 

 the original design with the result that the tunnel as com- 

 pleted follows a slightly sinuous path and is 14,536 m. long. 



The rocks met with for the first 3965 m. from the north 

 portal, near Kandersteg, consist nearly entirely of limestone 

 of Jurassic age. After this point the tunnel enters the 

 Gastern Granite, through which it runs for about 6400 m., 

 and from here to the southern portal, a distance of 4170 m , 

 crystalline schists of all classes are encountered. The speci- 

 mens employed were not uniformly distributed over the 

 whole length of the tunnel, most of them being from 

 the schistose rocks at the southern end, but some specimens 

 from the Gastern Granite and also from the Jurassic Lime- 

 stone Zone were also dealt with. 



Each rock was dealt with separately, as it was desired to 

 ascertain if there was any large variation of radium content 

 along the length of the tunnel. Unfortunately, however, 

 there is a gap in the results from 3545 m. from the south end 

 to 6415 m. from the north end — a distance of 4576 metres, 

 most of wdiich is in the Gastern Granite. No very striking 

 variation in radium content was detected along the length 

 of the tunnel, which agrees with the fact that apparently no 

 abnormal variations were met with in the thermal gradient, 

 as was the case in the St. Gothard Tunnel, in which the 

 abnormally high-temperature gradient at the northern end 

 of the tunnel was shown to coincide with rocks of a large 

 radium content *. 



The result for each specimen of rock is given and its 

 position in the tunnel in the following table. A table is 

 also shown giving the mean result for each class of rock 

 encountered. The radium content is given in billionths of a 

 gramme of radium per gramme of rock — i. e., the figure given 

 in the column for radium content has to be multiplied by 

 10~ 12 in order to reduce the result to number of grammes of 

 radium to one gramme of rock. 



* Joly, Phil. Mag-. Feb. 1912. 



