APPENDIX 278 



differentiate between those which are caused by sub- 

 sidences and those of volcanic origin. Volcanoes are not 

 confined to any one part of the world, but are to be found, 

 so far as latitude is concerned, pretty nearly everywhere; in 

 the Arctic Ocean, in the volcanic island of Jan Mayen, 

 between Iceland and Spitzbergen ; there are Mount 

 Erebus and Mount Terror in the Antarctic, besides very 

 numerous volcanoes in the Atlantic, Pacific, and Indian 

 Oceans, and their shores in both the temperate and torrid 

 zones. In all they are said to number, in a state of activity, 

 some three hundred. " Of these about two hundred and 

 fifty lie either on the borders of the Pacific, or on some of 

 its many islands. Thirty-nine either lie within or on the 

 borders of the Atlantic, of which thirteen are in Iceland, 

 or near the Arctic Circle, three in the Canaries, seven in the 

 Mediterranean Sea, six in the Lesser Antilles, and ten in 

 the Atlantic Ocean Islands. There are, however, a much 

 greater number of extinct volcanoes, which may at any 

 time again become active." (Houston, 1908.) 



The difficulty we are faced with is conveyed in the last 

 paragraph. Were it not for the uncertain number and 

 condition of extinct volcanoes, or rather of volcanoes 

 which have ceased for the time being to give any mani- 

 festation of activity, we might consider earth- currents in 

 their possible relation to areas liable to thermal dis- 

 turbances with a view to determining whether any con- 

 nection between them is suggested by their coincidence. 



One fact stands out prominently : thunderstorms 

 diminish in frequency towards the poles, and if they are a 

 factor in determining the occurrence and strength of earth- 

 currents of unusual tension one would expect to find a 

 minimum of disturbance towards the poles. I happen to 

 know, however, that in the neighbourhood of Port Arthur 

 a region admittedly volcanic the earth-current some- 

 times attains a potential of 500 volts. 



T 



