282 Prof. Norton on Molecular Physics. 



the magnetic W., except at the autumnal equinox, when they 

 will be nearly perpendicular to the needle. Tn the annual in- 

 equality, therefore, the needle should be in its most easterly 

 position at the vernal equinox, when the currents will be most 

 oblique to the needle, and at its most westerly position toward 

 the autumnal equinox. At Philadelphia and Toronto the secular 

 change is due to the excess of the N. to S. currents, from the 

 summer to the winter solstice, over the S. to N. currents from 

 the winter to the summer solstice. Under the influence of these 

 currents the needle should be in its most westerly position near 

 the winter solstice, or near the close of the period during which 

 the N. to S. currents are developed, and at its most easterly posi- 

 tion near the summer solstice. The observations at these sta- 

 tions give results in entire accordance with these theoretical con- 

 clusions. But for the influence of the currents at other localities, 

 the amount of the inequality should be equal to the annual 

 secular change. This was the case at Toronto (each 2') in the 

 years from 1845 to 1851. At Philadelphia the annual progres- 

 sion in 1843 was 4 ;, 4, more than double the annual inequality 

 (2'). This must be attributed to the preponderating action of 

 the currents traversing those localities at which the needle was 

 turning toward the west. 



Unequal Magnetic Intensities of the two Hemispheres. — This 

 has its origin in the unequal absolute velocities of the earth, near 

 the equinoxes, resulting from the progressive motion of the solar 

 system. A calculation from the most reliable data gives for the 

 ratio of the maximum velocity (March 4) to the minimum velo- 

 city (Sept. 6) 1'29. Now the vernal equinoctial currents deter- 

 mine the magnetic intensity of the southern hemisphere in high 

 latitudes, and the autumnal equinoctial currents that of the 

 northern hemisphere; and the ratio of intensities at the poles 

 (dip 90°) should be nearly equal to that of the maximum and 

 minimum velocities (1*29). According to Gauss's charts, its 

 actual value is 1*32*. 



[To be continued.] 



* It should have been stated in the text (p. 271), that the rotation of the 

 earth virtually shifts the point of normal impact of the aether to the east of 

 the 6 a.m. meridian, and so delays the morning critical hours. 



We propose to discuss, very briefly, in the next Number of Silliman's 

 Journal, the remaining topic of our memoir — Chemical Action. 



