ASTRONOMY AND METEOROLOGY. 407 



phere exceed those whose parhelia are in the southern in the proportion of 

 three to two, five to six, or nearly equal. The author calls the Great Circle, 

 which passes so as to divide the Milky Way pretty equally, the Galaxy 

 Circle. In the centre of this the Sun and Earth may be considered to be 

 placed ; it cuts the ecliptic towards the solstitial points, and is inclined to it 

 at about sixty dcg. He then finds that the planes of the orbits of the comets 

 aiv, for the most part, little, if at all, inclined to the plane of the Galaxy Circle, 

 r.:id that they go on decreasing in number as that inclination increases ; and, 

 therefore, he concludes that some cosmical cause must have led to such a 

 result. Also, the parhelia of by far the greatest number of those he has dis- 

 cussed arc found near the Galaxy Circle, showing that when they arc passing 

 most closely under the influence of the Sun they arc both near the Galaxy 

 Circle, and their proper motion is nearly parallel to its plane. Hence the 

 greater number of comets come to us from the region of the Galaxy itself. 



THE DIVISION OF EIELA'S COMET. 



BY D. VAUGHAX. 



The forces which occasionally disturb the tranquillity of our atmosphere, 

 must have a wide field for their operation in the vast expanse of aeriform 

 matter, which constitutes the principal part of comctary bodies. Like all 

 light bodies, the air we breathe is very sensitive to electrical attraction and 

 repulsion ; and this becomes a frequent cause of storm. Wherever the prev- 

 alence of moisture makes the superfluous electricity descend from the region 

 of the clouds to the ground, the air is repelled, and forms an ascending cur- 

 rent. As it undergoes expansion during the ascent, the cold which this 

 occasions condenses the accompanying vapor ; so that descending drops of 

 rain diffuse moisture through the medium which they traverse, and thus im- 

 prove its conducting power. Accordingly, the discharges of electricity are 

 constantly repeated, and the aerial current continues to ascend, while the sur- 

 rounding air presses on to the scene of action, and participates in the great 

 movement. Such is Dr. Hare's theory of storms ; but some part must be 

 ascribed to the heat evolved by the condensation of the watery vapor. 



If the small quantity of dense matter which is required to hold together 

 the rare comctary gases, contained a large proportion of water or some other 

 volatile substance, much vapor should be generated on the approach of the 

 comet near the sun. Whenever tin.; vapor condensed, at the place screened 

 from the solar rays or in anv other locality, a discharge of electricity would 



v ti * ' ' 



occur between the envelop and the central mass of the comet, while ascend- 

 ing currents of air commenced in the rare fluid, and determined the focus of 

 a storm. Owing to its vast height, the greater part of the nebulous appen- 

 dage would participate in the movement, and give it a degree of impetuosity 

 which the feeble attractive power of the nucleus could scarcely control. If 

 ascending currents of air on our own planet prevent condensed vapor from 

 falling until it forms large drops of rain, hailstones of considerable size, and 

 in some case?, waterspouts ; the vapor returning to a liquid state in the at- 

 mosphere of a comet, where gravity is many thousand times more feeble, 

 might be sustained by similar ascending currents, until it had collected into 



