Remarks on the Tails of Comets. 65 



sat remarked the undulations of the tail of the comet in 1618, 

 Hevelius observed the same in the tails of the comets in 1652 

 and 1661. M. Pingre took notice of the same appearance in the 

 .comet of 1769." 



That the streamers of the Aurora, to the popular gaze, resem- 

 ble the tails of comets, is very evident ; and there ends the affin- 

 ity. As well might the resemblance of stars to planets be addu- 

 ced as proof of their identity. The apparent agitation in the 

 light of a comet's tail, extends through its whole length, from 

 fifty to one hundred millions of miles, in a single second of time. 

 Now this fact is entirely incompatible with the established and 

 well known rate of the velocity of light, which gives several se- 

 conds of time to its transit through a few millions of miles. This 

 shooting of light is without question to be attributed to fluctua- 

 tions in our own atmosphere, and is merely another form of the 

 twinkling of the stars. The successive changes in the planet 

 Mercury, when seen by the naked eye, in a clear and bright twi- 

 light, present analogous phenomena. The star Capella, when 

 near the northern horizon, is often noticed to change from the 

 first to the fourth magnitude in regular and successive periods of 

 nearly a second's duration. " Concerning the sudden and uncer- 

 tain fluctuations of the tails," says Newton, " I here say nothing, 

 because they arise from the obscuring vapors and changes in our 

 atmosphere." An additional proof of this, is the fact that these 

 streaming appearances are not to any extent visible except at low 

 altitudes. In the cases alluded to by Prof. Vince, two, certainly, 

 could never have been seen by the observers in their own country 

 at a high altitude. The others I have not investigated. 



Equally unsound is the idea that electricity has any agency in 

 the matter. In reference to the tails of comets, there is not the 

 slightest evidence of electrical action, "and those theories," says 

 an ingenious writer, " which attribute this phenomenon of the Au- 

 rora to electricity, are met by the following unanswerable objec- 

 tions. The electric fluid never accumulates in visible cohesive 

 masses ; it is always dispersed through the earth and air, and its 

 tendency is to remain in equilibrio, or nearly so, unless when col- 

 lected by some medium diff'erent from the atmosphere, as in thun- 

 der clouds. The electric fluid never undulates or waves to and 

 fro in sinuous curves and motions, nor does it settle in banks of 



Vol. XL, No. 1.— Oct.-Dec. 1840. , 9 



