PRESIDENTIAL ADDRESSES. 521 



helmshaven, the horizontal force was above par by 

 0-00075, 0-00088, and 0-00090 (C.G.S. in each case) 

 at 2.10 P.M. ; and below par by 0-0007, 0*00066, 

 0-00075 at 3 o'clock. The mean value for all the 

 eleven places was nearly 0*0005 above par at 2h. 

 iom., and 0-0005 below par at 3h. The photo- 

 graphic curves show changes of somewhat similar 

 amounts following one another very irregularly, 

 but with perfectly simultaneous correspondence at 

 the eleven different stations, through the whole 

 eight hours of the storm. To produce such changes 

 as these by any possible dynamical action within 

 the sun, or in his atmosphere, the agent must have 

 worked at something like 160 million million 

 million million horse-power 1 (12 x io 35 ergs per 

 sec.), which is about 364 times the total horse- 

 power (3-3 X io 33 ergs per sec.) of the solar radia- 

 tion. Thus, in this eight hours of a not very 

 severe magnetic storm, as much work must have 

 been done by the sun in sending magnetic waves 

 out in all directions through space as he actually 

 does in four months of his regular heat and light. 

 1 i horse powe* - 7-46 x io 9 ergs per second. 



