( 781 ) 



generated is made possible by tliese results for deeper strata too. 

 On the diagrams obtained at Batavia when the earth-current is 

 registered, there are a few cases of an initial impulse and as the time 

 unit was very ample (1 millim. = 1 min.) and moreover as the 

 magnetic component too was registered with great sensitiveness, these 

 cases are very instructive. 



Date Initial movement of the ^-TFearth- 



and current commences before that of 



Hour. the magn. North-component. 



J4May 1906, 4'' a.??i. Bat. T 0.0 min. Commenc. gradual 



30 July „ 3 „ 



3 September ,, 1 p.m. 



11 ,, ,, o ,, 



10 November ,, 12 ,, 



26 ,, ,, 1 am 



26 December ,, 11p.m. 

 8 January 1907 12 „ 



15 ,, ,, 3 am. 



14 February ,, 3 ,, 



27 January 1908 9^.?/i. 



0.6 

 0.0 

 0.0 

 0.0 

 0.0 

 0.0 

 0.0 

 0.0 

 0.0 

 0.0 



pretty sudden 

 sudden 

 pretty sudden 

 sudden 



pretty sudden 

 sudden 



With the exception of one case, where indeed the determination 

 of the time was less accurate on account of the gradual commence- 

 ment of the initial movement, we thus tind simultaneousness for the 

 initial movement for earth-current and magnetic vector. 



As has often happened, we must change a hypothesis of explanation 

 formed on first getting acquainted with the facts, when later on we 

 have arrived at a more extensive knowledge of the facts by extension 

 of the material. 



This is the case here too. 



Though I at first thought to find the seat of the current of electricity 

 which is supposed to generate the initial impulse in the highest layers 

 of the atmosphere, the nature now revealed of the vertical component 

 induces me to look for the seat rather in the earth itself. 



At the outset the current must be in general an East- West current 

 of positive or West-East of negative electricity, because everywhere 

 the horizontal magnetic component increases. The situation and form 

 of that current seems to be variable and to undergo a gi-eat influence 



53 



Proceedings Royal Acad. Amsterdam. Vol. X. 



