32 M. Arago on the Comet of 1835. 



calculations, the derangements or perturbations which the comet 

 at present expected, and known by the name of Halley's comet, 

 must encounter during its progress, from the united attractions 

 of Jupiter, Saturn, Uranus, and the Earth, Messrs Damoiseau 

 and De Pontecoulant fixed, the one the 4th, the other the 7th 

 November, for the time of the comet passing its perihelion, that 

 is, the point of its orbit which is nearest the sun. Since these 

 first researches, astronomers have determined, that the mass of 

 Jupiter, which had been considered as equal to the 1070th part 

 of that of the sun, is equal to the 1054th part. By adapting 

 this new calculation, and by taking more completely into ac- 

 count the action of the earth, M. de Pontecoulant has definitely 

 fixed the passage of the perihelion for the 13th instead of the 

 7th November. 



At the moment of this passage, the distance of die comet from 

 the sun will not exceed six-tenths of the distance of the sun from 

 the earth. At the other extremity of the great axis of the orbit, 

 in thirty-nine years from this time, the distance of the two 

 heavenly bodies will on the contrary be immense. Calculation 

 gives more than thirty-five times the radius of the terrestrial 

 orbit, that is, more than thirty-five times the distance of the 

 earth from the sun. 



The result of the calculation of the passage of its perihelion 

 by Halley's comet in 1835, compared with the result of observa- 

 tion, will inform us if this comet, like the small and feeble one 

 which returns at short intervals, is sensibly deranged during its 

 progress by the resistance of the ether. This comparison, in its 

 turn, will furnish us with some notions on the physical constitu- 

 tion of the comet which we expect, for a given resisting medium 

 exercises more or less effect according to the volume and density 

 of the body which traverses it. 



Is the ether in repose, or does it move round the sun, from 

 west to east, in the manner of the planets ? In the last case, its 

 effect on the comet, which retrrns at short intervals, which itself 

 moves from west to east, will be different from that which it 

 will exercise on the comet of Halley, whose motion, on the con- 

 trary, is directed from east to west. The science of celestial 

 movements, and that of cosmogony, are equally interested in the 

 solution of the problem to which I allude. 



