Prof. Norton on Molecular Physics. 275 



This conception of the origin of the irregular disturbances 

 links them theoretically, as they are in fact, on one side with 

 the physical changes observed in the photosphere of the sun, 

 and on the other with the auroral phenomena that occur in 

 the photosphere of the earth. It contemplates the corusca- 

 tions of the aurora and the sympathetic tremblings of the mag- 

 netic needle, as but one phase of the "magnetic storm" of 

 subtile vapour that descends upon the earth from the regions 

 of space. 



One of the most conspicuous facts relative to the disturbances 

 under consideration is, that the disturbances of the horizontal 

 force that diminish its intensity prevail, at all hours, over those 

 which augment it. This fact may be attributed, from our pre- 

 sent stand-point, to the circumstance that the descending masses 

 of auroral matter, in receiving the velocity of rotation of the pho- 

 tosphere of the earth, must generate electric currents or pro- 

 gressive waves directed toward the west. There is still another 

 effect that theoretically should result from the arrival of these 

 cosmical masses. The electrical excitation that should thereby 

 be produced in the photosphere will act indirectly, in a greater 

 or less degree, upon the earth's surface, and develope currents 

 running over it in every direction from the locality immediately 

 underneath the region of excitation in the upper atmosphere. 

 The increase in the morning maximum of horizontal force in the 

 years of greatest disturbance gives indication of the existence 

 of this effect. The tendency of such currents will be almost 

 identically the same with the currents we have supposed to be 

 directly developed in the earth's crust by the impact of the sether 

 of space. 



The electrical action upon the crust of the earth here consi- 

 dered may be in a great degree direct rather than inductive; 

 that is, the penetration of the subtile cosmical matter into the 

 earth's photosphere may occasion streams of electricity in the 

 direction of the impact that may penetrate the atmosphere and 

 take effect upon the earth's surface. The physical cause here 

 supposed to be in operation should cooperate with the others 

 that have been noticed in determining regular variations of the 

 declination and directive force that would be observable in the 

 mean daily variations for a month or a year, even after these 

 have been freed from the greater disturbances. 



It is conceivable that the effects which have been ascribed to 

 the radial photospheric currents might be produced by an ana- 

 logous system of currents within the earth's crust directed 

 toward the region directly underneath the sun. But no plausi- 

 ble cause can be assigned for the existence of such currents, 

 since, if the sun be supposed to produce tides in the vast sea of 



