ASTRONOMY AND METEOROLOGY. 413 



expresses a hope that observation will furnish data sufficient to confirm 

 his theory. As to the instantaneous separation which was observed in 

 Asteius's comet, M. Faye attributes it to a totally different cause, which he 

 endeavors to explain by the following supposition, namely, that were the 

 nucleus of Donati's comet suddenly to cease emitting the particles which 

 form the tail, the latter would be rapidly separated from the nucleus, and 

 form a second comet, which would follow a hyperbolical orbit, while the 

 nucleus, surrounded only by a slight nebulosity, would continue its elliptical 

 route. A commencement of such a separation took place in the great comet 

 of 1843, and such might easily have been the case with the comet of Aste- 

 ius, mentioned by Ephorus. 



THE DIVISION OF BIELA'S COMET. BY D. VAUGHAX. 



The aeriform matter of which comets are almost entirely composed, must 

 furnish a wide field for the play of those forces which occasionally disturb 

 the tranquillity of our atmosphere. So light is the air we breathe, that its 

 Aveight is considerably altered by electric action; and from this cause storms 

 frequently arise. Whenever the prevalence of moisture causes the superflu- 

 ous electricity to escape from the region of the cloiids to the ground, the air 

 is repelled, and forms an ascending current. As it undergoes expansion 

 during the ascent, the cold which- this occasions condenses the accompany- 

 ing vapor; and descending drops of rain diffuse moisture through the me- 

 dium which they traverse, and improve its conducting power. Accordingly 

 the discharges of electricity are constantly repeated, and the aerial current 

 continues to ascend; while the surrounding air presses into the scene of 

 action, and participates in the movement. Such is Dr. Hare's theory of 

 storms. 



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

 the rare cometary gases, contained a large proportion of water, or any other 

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

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

 from the solar rays, or at any other locality, a discharge of electricity would 

 occur between the envelop and the central mass of the comet; while an 

 ascending current commenced in the rare fluid, and determined the focus of 

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

 age would take part 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 a considerable size, 

 and in some cases waterspouts, the vapor returning to a liquid form in the 

 vapor of a comet, whose gravity is very feeble, should be sustained by simi- 

 lar ascending currents, until it had collected into bodies as large as lakes or 

 seas. Even large collections of the fluid, evaporated from the central nu- 

 cleus, may be sometimes driven beyond the sphere of its effective attraction, 

 and may separate forever from the comet, taking away its share of the 

 aeriform appendage. 



That the division of Biela's comet arose from a cause of this nature, is 

 proved by a singular fact. The t\vo parts into which this body divided were 

 almost equal in size and brilliancy when nearest to the sun; but at a more 

 considerable distance from him, one was about eight times as large as the 

 other, and about four times as bright. This shows that they differed in 



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