46 H. I. JENSEN. 



or even ordinary electricity. When, however we consider 

 that the earth as a whole behaves as a magnet, and that 

 the earth's atmospheric magnetism is instantaneously 

 influenced by solar prominences, that magnetism, heat and 

 electricity are transmutable forms of energy, and that 

 many ferruginous volcanic lavas are fair conductors of 

 magnetism, it becomes quite feasible that the sun's radiant 

 energy should penetrate the earth's crust rapidly, and once 

 having reached the volcanic foci, be transformed into heat. 

 In order that this transformed energy might again escape, 

 conduction through rock masses, a very slow process, would 

 be essential. As I have already before suggested, there 

 may also be solar rays 1 which are quite capable of permeat- 

 ing rock masses without producing any heating effect until 

 they meet with conditions favourable for their transmuta- 

 tion. Rock masses would then be warmed, not by the 

 direct solar radiation, but by heat conducted from foci 

 within where transformation of energy can take place, a 

 process analogous to the heating of our atmosphere, which 

 is effected chiefly by heat conducted from the earth's sur- 

 face and not by the direct solar rays. 



Increase in the amount of solar heat received by the 

 earth (as at sunspot maxima) may also have the direct 

 effect of checking the leakage of heat from the earth's 

 surface by radiation into space, and this diminution of 

 leakage will tend to check somewhat the outward creep of 

 heat in the earth's crust by conduction. Thus the amount 

 of pent up heat in volcanic foci is increased, its slow escape 

 being hampered. In this way alone can we explain why 



1 Compare also the recent investigations by the Curies and 

 Rutherford on the penetrating powers of the a, /? and y rays of the 

 new radioactive elements. A recent paper by Sir Norman 

 Lockyer — " Simultaneous Solar and Terrestrial Changes," (Nature, 

 Feb. 11th 1904) — will also be read with interest in connection 

 with the above discussion on terrestrial magnetism. 



