122 



vapour, like the aurora borealis, moving by the polar currents 

 of the sun, it would necessarily move nearly at right angles to 

 the orbit ; such are their paths. If, again, we consider them as 

 mere magnetic sparks, they must be conveyed by the polar cur- 

 rent to the attractive pole, and issue out again at the negative 

 pole, and thus continue their circular motion from and to the 

 axis of the sun by the magnetic currents. The light of the sun 

 is too intense to examine minutely the effects of these bodies 

 near it ; probably in passing through the axis they present the 

 appearance of a solar aurora borealis and australis. 



The following description in Sir J. Herschel's ' Astronomy 7 

 is interesting : — 



C( Their variations in apparent size during the time they con- 

 tinue visible, are no less remarkable than those of their velocity : 

 sometimes they make their first appearance as faint and slow 

 moving objects, with little or no tail; but by degrees accelerate, 

 enlarge, and throw out from them this appendage, which in- 

 creases in length and brightness till they approach the sun and 

 are lost in its beams ; after a time they again emerge on the 

 other side, receding from the sun with a velocity at first rapid, 

 but gradually decaying. It is after thus passing the sun, and 

 not till then, that they shine forth in all their splendour, and 

 that their tails acquire their greatest length and development, 

 thus indicating plainly the action of the sun as the exciting cause 

 of that extraordinary emanation." 



A singular circumstance has been remarked respecting the 

 change of dimensions of the comet of Encke in its progress to 

 and from the sun, viz. that the real diameter of the visible ne- 

 bulosity undergoes a rapid contraction as it approaches, and an 

 equally rapid dilatation as it recedes from the sun, owing probably 

 to its passage through the axis. Cometary bodies may appear, in 

 looking at them in the heavens, irregular and capricious in their 

 paths ; but a careful observation will show that they uniformly 

 move to the same pole and emerge from the opposite. They 

 may also pass through the axis of the planets in a similar man- 

 ner, thus producing the phenomena of the aurora borealis and 

 australis. (See Plate III.) 



To conclude, we may reasonably consider that by this power 

 the stability of the solar system is maintained, and the form of 



