42 LIGHT SCIENCE FOR LEISURE HOURS. 



would seem rather to the influence of mass and prox- 

 imity that the magnetic disturbances caused by the 

 moon must be ascribed. But if the moon exercises an 

 influence in this way, why should not the planets? 

 "We shall see that there is evidence of some such in- 

 fluence being exerted by these bodies. 



More mysterious, if possible, than any of the facts 

 we have discussed is the phenomenon of magnetic 

 storms. The needle has been exhibiting for several 

 weeks the most perfect uniformity of oscillation. Day 

 after day, the careful microscopic observation of the 

 needle's progress has revealed a steady swaying to and 

 fro, such as may be seen in the masts of a stately ship 

 at anchor on the scarce-heaving breast of ocean. Sud- 

 denly a change is noted ; irregular jerking movements 

 are perceptible, totally distinct from the regular peri- 

 odic oscillations. A magnetic storm is in progress. 

 But where is the centre of disturbance, and what are 

 the limits of the storm ? The answer is remarkable. 

 If the jerking movements observed in places spread 

 over very large regions of the earth and in some well- 

 authenticated cases over the whole earth be compared 

 with the local time, it is found that (allowance being 

 made for difference of longitude) they occur precisely 

 at tKe same instant. The magnetic vibrations thrill in 

 one moment through the whole frame of our earth ! 



But a very singular circumstance is observed to 

 characterize these magnetic storms. They are nearly 



