' Prof. Norton on Molecular Physics. 271 



toward the east. Strictly the two sets of ecliptic currents, the 

 one having an easterly and the other a westerly trend, will be 

 developed at various points on one side and the other of the 

 circle of intersection with the earth of a plane passing through 

 the most advanced point and the geographical pole. The special 

 currents developed on the circle perpendicular to this will have 

 the greatest intensity on the side opposite to the sun, as already 

 shown. The effects of the diverse currents, originating in the 

 impulsive action of the aether of space upon the preceding half 

 of the earth, are conspicuously observable in the variations of 

 the declination and horizontal force during the last, half of the 

 night and the earlier part of the day. As the day advances, the 

 radial photosphericcurrents (sceSilliman's Journal, vol. xix. p. 190) 

 come into more effective action, and greatly modify the magnetic 

 variations that would result from the currents just mentioned. 

 They augment the diminution of the horizontal force in the fore- 

 noon, and deflect the needle further to the west at midday*. 

 They are also the principal cause of the increase of the horizontal 

 force in the afternoon. The change of the hours of the morning 

 maxima and minima with the seasons is mainly a consequence 

 of the changes experienced, during the year, in the position of 

 the circle of the earth perpendicular to the radius of the earth's 

 orbit at 6 a.m., with respect to a meridian passing through 

 the most advanced point of the earth's surface at that hour. 

 The circle in question coincides with the meridian at the two 

 equinoxes, is inclined 23^° to it on the west side at the summer 

 solstice, and under the same angle on the east side at the winter 

 solstice. In consequence of the change of position of this circle, 

 the radial currents tend to alter the critical hours above referred 

 to. For the rest, it should be observed that the phenomena 

 all show that the temporary currents by which they are pro- 

 duced do not come into most effective action until a certain in- 

 terval of time after the moment of most intense excitation, be- 

 cause, doubtless, of the residual currents that continue in action 

 with diminishing energy. 



The two sets of currents that have been specified afford a 

 complete explanation of the observed periodical variations of 

 the declination and directive force of the magnetic needle. In 

 considering their separate action it is to be distinctly observed, 

 (1) that the currents produced in the earth's crust by the impul- 

 sive action of the aether of space are developed at each station 

 between the hours of midnight and noon, though the currents 

 thus excited will be propagated on and produce a certain effect 

 at other stations before midnight and after noon ; (2) that the 



* The special effects here alluded to, and in general the effects referred 

 to in what follows, are those observed in our latitudes. 



