90 



THOUGHTS ON THE INFLUENCE OF ETHER 



The comet which, during the last century and a half, has, more than any other, given 

 rise to the speculation, the calculation, the wonder, and the triumph of astronomers, is 

 unquestionably that of Halley. 



The comet in question furnishes us with a single known exception to the law, that as 

 comets approach the sun the splendor of their tails increases, and after passing their peri- 

 helia gradually diminishes to their final disappearance. 



History records eight different visits of Ilalley's comet to its perihelion, from the year 

 1305 to 1835 inclusive. 



The inclination of this comet to the ecliptic is less than eighteen degrees, and its peri- 

 helion distance about half the radius of the earth's orbit. The comet, while approaching 

 and receding from its perihelion, must, therefore, have passed through that part of the 

 solar system where the ascending current of ether exists in greatest force. 



If the ethereal current have any power to detach the tail of a comet from its nucleus, 

 by the force of its blast, we might suppose it should be conspicuously displayed upon 

 Ilalley's comet. 



During five of the visits of Ilalley's comet to its perihelion, we have the testimony of 

 the contemporary astronomers that the tail diminished or disappeared on approaching the 

 sun, or that it reappeared and expanded after passing the nearest point to that orb. Sir 

 John Hcrschel, in the year 1835, recorded both of these phenomena.* 



* Ilalley's comet passed its perihelion June 8th, A. D. 1456. I extract from "Pingre's Cometographie" the 

 following notices of this visit of the comet : 



"Although two Polish historians assure us that the size of this comet had not appeared great in Poland, all 

 others agree in representing it as grand, terrible, of an extraordinary size, and carrying in its train a tail which 

 covered two signs, or sixty degrees." 



" This tail, however, was not always of the same length : it was observed of thirty spans ; it was observed of 

 more than one hundred spans ; sometimes no trace of a tail could be seen." (Vol. i, p. 459.) 



The 6th June the length of the tail was twenty-two degrees, (p. 461.) 



" Another contemporary historian says, the 3d June, the tail was ten degrees, as he satisfied himself with instru- 

 ments." (p. 461.) 



" At Bologna, in Italy, where the latitude is 44° 30', the comet get, but for a short time, its tail, moreover, 

 after having entirely disappeared, was about to reappear. No devait pas tardcr a reparaitro." (p. 462.) 



In 1531 Ilalley's comet passed its perihelion August 24th. Pingre says, "The most valuable observations we 

 have of the comet of 1531, are those of Apian, the astronomer of the Emperors Charles V, and Ferdinand I. He 

 began his observations the 13th August. He noticed that in general the tail was opposite the sun, and that it 

 disappeared when the comet approached the horizon, so that he thought at first that a cloud obscured the view." 

 (Vol. i, p. 487.) 



Inasmuch as the tails of comets become brighter on approaching the horizon in their diurnal motion, owing to 

 the increasing darkness, I conclude that the astronomer Apian must have referred to the comet's orbital motion, 

 which is equivalent to saying that as the comet approached the sun, its tail disappeared. 



