Chase.] 488 [December. 



Since the principal agency of the sun in producing currents and 

 barometric fluctuations appears to reside in the heat of its rays, and 

 that of the moon in its diiferential or tidal attraction, it seems very 

 probable that the ratio of the barometric to the magnetic disturbance 

 of each luminary may be some function of the relative barometrical 

 and tidal effects of the two bodies. This hypothesis is confirmed by 

 the fact that the lunar-diurnal variations, both of the magnet and of 

 the barometer, exhibit two high and two low daily tides, while the 

 solar-diurnal magnetic variation, like the temperature-tide of the 

 barometer, has only one maximum and one minimum in twenty-four 

 hours. 



Let A = the tidal-current variation of equilibrium. 

 B = the diurnal barometric variation. 

 M = the diurnal magnetic variation. 



Let the solar elements be distinguished by A', B', M' ; the lunar 

 by A", B", M". 



If the modern physical hypotheses are correct, and the forces that 

 produce A, B, and M are all forms of motion, it is probable that 

 some simple relationship may exist between them. In endeavoring 

 to ascertain that relationship, we readily discover that 



A' < A" 

 B' < M' 

 B' > B" 

 B" > M" 



These inequalities, together with the fact that the solar currents 

 are developed in air that is disturbed by the greater attractive energy 

 of the moon, and the lunar currents in air that is disturbed by the 

 more powerful barometric action of the sun, suggest the supposition 

 that B may be a mean proportional between A and M, and that we 

 may therefore have the following equivalent proportions : 



B' : B" : : ^ K' M' : 7 A" M" 

 A' : A" : : B'^ M" : B"' W 

 W : M" : : B'^ A" : B"^ A' 



From the same considerations, we may readily infer that 



-- = - a) 



M' A" ^^ 



and that,.*., B" is a mean proportional between B' and M". 



According to Maj.-G-en. Sabine's tables (St. Helena Obs., vol. ii, p. 

 Ixi), there is a solar maximum, measured in parts of the total force, 



