182 HENRY A. KOWLAND 



Hence the earth must be electrified to a potential of about 



41 X 10 15 volts * 



in order, under the most favorable circumstances, to account for the 

 earth's magnetism. This would be sufficient to produce 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 I 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 mis- 

 take 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 



r- V * 

 ~ 8*a* ' 



which amounts to no less than 



1,800,000 grms. 



per square centimetre! or 10,000 kil. per square inch! Such an electro- 

 static force as this would undoubtedly tear the earth to pieces, and dis- 

 tribute its fragments to the uttermost parts of the universe. If the 

 moon were electrified to a like potential, the force of repulsion would 

 be greater than the gravitation attraction to the earth, and it would 

 fly off through space. 



For these reasons I rejected the theory, and now believe that the 

 magnetism of the earth still remains, as before, one of the great mys- 

 teries of the universe, toward the solution of which we have not yet 

 made the most distant approach. 



4 That this is not too great may be estimated from my Berlin experiment, 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 T] ^ ffTr 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 formulae show that 

 two spheres of unequal size, rotating with equal angular velocity and charged to the 

 same potential, produce the same magnetic force at similar points in the two systems. 



