ISBS.] 375 [Chase. 



solution, 1)}^ approach, b}' pressure, by combination, by crystal- 

 lization, by revolving currents, by either of the various known 

 methods, there is an immediate effort on the part of all the 

 forces acting either within or upon the disturbed bodies to 

 adapt themselves to the new conditions. If the effort is unre- 

 sisted, the adaptation may be as rapid as the disturbance, and 

 there may be no evidence of electric excitement. In all cases the 

 amount of electric manifestation seems to depend on the amount 

 of precedent resistance. 



In ordinary electric and magnetic experiments the equilibrat- 

 ing or manifesting force appears to be molecular, and for many 

 l^lausible reasons it has often been supposed to be the same as 

 is exhibited under different forms as cohesion, crystallogeny, 

 and chemical affinity. Terrestrial magnetism is a cosmical 

 manifestation, and as a cosmical equipoising force exists in 

 gravitation, it is difficult to conceive any cogent reason for vio- 

 lating the law of parsimony by supposing an additional force 

 for accomplishing the same ends. We have seen that disturb- 

 ances which are transmitted with the most various degrees of 

 rapidity, disturbances of gravitation, of light, of heat, of mo- 

 tion or position relative to the sun or moon, of atmospheric 

 moisture, of electric condition, or of simple physical rest, may 

 be followed by magnetic displays. In the most frequent of these 

 disturbances the motion is greater than that of undulation, in- 

 volving an actual progression of aerial particles, but whether 

 the molion be rapid or sluggish, undulatory or progressive, 

 gravitation acts with inconceivable rapidity* towards the planes 

 of equilibrium. 



A joint consideration of the gyroscopic, viscous, elastic, cen- 

 trifugal and centripetal forces which are indicated by the baro- 

 meter, shows that the contour of the atmosphere is such as Avould 

 be assumed if the changing motions relatively to the sun acted 

 as disturbances, and the terrestrial gravity as a restorer of 

 equilibrium (ante, vol. ix, p. 283, seq.).t 



* According to Laplace's estimate the velocity of gravity is at least six 

 raillion times as great as that of light. 



f When I first called attention to this point, I had seen only the second 

 volume of the St. Helena Observations. I subsequently met with the 

 first volume, containing (on p. 88) General Sabine's means of five years 

 observations, whicli show a daily barometric range from + .037 to — 



