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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 
hear the northern horizon, is often noticed to change from t 
first to the fourth magnitude in regular and successive periods of 
ea 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 
ata 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- 
tora to electricity, are met by the following unanswerable objec- 
“ions. '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 different from the atmosphere, as in thun- 
der clouds. The electric fluid never undulates or waves: to and 
TO In sinuous curves and motions, nor does it settle in banks of 
Vol. xx, No. 1.—Oct.-Dec, 1840 9 
