Chase.] ^66 [October. 



It is interesting, especially if we incline to adopt the common 

 hypothesis that the barometric fluctuations are all owing, mainly, if 

 not exclusively, to thermal disturbances, to observe that the mag- 

 netic force is more directly and powerfully aff"ected by variations of 

 temperature than the barometric pressure; and that at St. Helena 

 the relation of the barometric to the thermometric movements is less 

 marked than those of either the horizontal or vertical force to the 

 fluctuations of gravity and of temperature. The relative preponde- 

 rance of the rotation tide over the temperature tide at St. Helena 

 (as shown by the barometer), is an additional evidence of the eligi- 

 bility of that station for observing the correspondence between the 

 fluctuations of magnetic force and the disturbances of gravitation. 



In comparing the St. Helena and Toronto totals, five of the 

 columns exhibit an opposition of relations, such as might have been 

 anticipated, because the laws of equilibrium require that a disturbed 

 " line of force" in one portion of the globe should be counterbalanced 

 by an opposite line in another portion. 



The analogies that have been pointed out by Sir David Brewster 

 and Sir John Herschel, between the curves of terrestrial magnetism 

 and those of the polarization of skylight, are a natural consequence of 

 the mechanical laws which we have been considering. The special 

 maximum which Herschel finds is so diflScult to account for (Meteor- 

 ology, p. 2o0), may be explained by the centripetal reaction against 

 the centrifugal thermal and other solar disturbances, which is a 

 maximum at 90° from the sun. 



Pending nominations 540, 541, were read. 

 And the Society was adjourned. 



