1868.] 373 [Chase. 



is barometric and not magnetic, for the ordinary thermal inllu- 

 ence on the barometer is overridden by the inflnences of atmos- 

 pheric cnrrents and terrestrial absorption and radiation, of 

 which I have treated in discussing the laws which regulate the 

 transmission and distribution of solar heat {ante^ pp. 2(5 1-209, 

 309-315). 



It appears, therefore, that the variations of declination are 

 greater in summer than in winter, greater by day than at night, 

 greater at sunrise than at sunset (see infer alia, Hobarton 

 Mag. and Met. Obs., v. ii, plate 1), greater at aphelion than at 

 perihelion, greater at the equinoxes than at the solstices, 

 greater at the N. autumnal than at the N. vernal equinox, 

 greater in auroras and thunder-storms than in electric calms, 

 greater at the lunar syzygies than at the quadratures, greater 

 at low barometer than at high barometer, greater at the theoreti- 

 cal hours of high tide than at those of low tide (see Sabine's 

 and other discussions of the lunar-diurnal variations), greater 

 at full moon than at new moon, in fine, greater in the presence 

 than in the absence of various violent local agitations. 



The existence of magnetic rays in the spectrum, and the self- 

 registering records which demonstrate the simultaneous occur- 

 rence of disturbances in the solar photosphere and in the earth's 

 magnetic atmosphere, seem to indicate an influence which is 

 transmitted with a velocity at least as great as that of light ;* the 

 controlling power of thermal changes was early recognized, and 

 Norton even submitted it to the test of calculation (Silliman's 

 Jour. [2] vols. 4, 8, &c.) ; the amount of electricity contained 

 in a single drop of w^ater has been computed by Faraday and 

 others, who have shown that the electric disturbances during 

 evaporation, condensation and convection are surprisingly 

 great ;f the influence of thunder-storms and other electric 

 meteors might reasonably have been predicted a priori, as soon 

 as the intimate relations of magnetism and electricity were as- 

 certained ; Faraday sought in vain for some experimental proof 



* The magnetic relations of light suggest a reference to the (perhaps 

 accidental) relation of light to terrestrial gravitation, which I pointed 

 out in a former communication [ante, p. 2(59). 



f The arguments by which this conclusion has been attacked do not 

 disprove the disturbances, but they merely show that in many cases the 

 equilibrium is restored as soon as it is broken. 



