of the -Earth? s Magnetism. 105 



As the earth makes one revolution in 23 h 56' 4", or in 

 86164 seconds, we have 



2tt . 

 ™ = 86164' 

 and 



n = 299,000,000,000* millims. per second. 

 Hence the earth must be electrified to a potential of about 



41 x 10 15 voltsf 

 in order, under the most favourable circumstances, to account 

 for the earth's magnetism. This would be sufficient to pro- 

 duce a spark in atmospheric air of ordinary density of about 



6,000,000 miles ! 

 Professors Ayrton and Perry have only found the potential 

 10 8 volts, or 400,000,000 times less than 1 find it. 



It was this large quantity which caused me to reject the 

 theory; for I saw what an immense effect it would have in 

 planetary perturbations ; and I even imagined to myself the 

 atmosphere flying away, and the lighter bodies on the earth 

 carried away into space by the repulsion. And, doubtless, had 

 not Professors Ayrton and Perry made some mistake in their 

 calculation by which the force was diminished 16 x 10 16 times, 

 they would have feared like results. 



For according to Thomson's formula, the force would be 

 equal to a pressure outwards of 



V 2 



r== o 2> 



OiraT 



which amounts to no less than 



1,800,000 grms. 

 per square centimetre ! or 10,000 kil. per square inch ! 

 Buch an electrostatic force as this would undoubtedly tear the 

 earth to pieces, and distribute its fragments to the uttermost 

 parts of the universe. If the moon were electrified to a like 



* From a preliminary calculation of a new determination made with 

 the greatest care, and having a probable error of 1 in 1300. 



t That this is not too great may be estimated from my Berlin experi- 

 ment, where a disk moving* 5,000,000 times as fast as the earth with a 

 potential of 10,000 volts, produced a magnetic force of ro ^ of the earth's 

 magnetism, 



5,000,000 x 10,000 X 50,000 = 2,500,000,000,000,000, 



which is of the same order of magnitude as the quantity calculated, 

 namely 61 x 10 15 . It can be seen that this reasoning is correct, because 

 the formulas show that two spheres of unequal size, rotating with equal 

 angular velocity and charged to the same potential, produce the same mag- 

 netic force at similar points in the two systems. 



