327 
ON THE FORMATION OF THE TAILS OF COMETS. 
By M. FAYE.* 
I N the Comptes Mencius of June 27, 1 read, not without surprise, 
a note by M. Flammarion, in which the learned author 
throws doubt upon the materiality of the tails of comets, and 
the existence of the repulsive force which produces them, a 
force the principal characters of which were formerly indicated 
by me. 
It is curious that these denials appear in the same number 
of the Comptes Mendus as the spectroscopic observations of 
MM. Huggins, Wolf, and Thollon, which show in the analysis 
of the light of the present comet the super-position of two 
spectra, evidently due to the presence of material molecules, 
some reflecting the light of the sun, the others also emitting a 
light of their own. Moreover, this is what spectrum analysis 
has proved for all comets, without exception. 
The argument upon which M. Flammarion depends recurs 
to the idea that the comet carries its tail as a sort of brush con- 
tinuous with itself. He concludes that the extremity of this 
brush must sweep through space with the frightful velocity of 
16,000 leagues per second; and in consequence the above- 
mentioned brush is not a body, but an appearance, a sort of 
luminous phantom due to the excitation of the ether situated 
behind the comet. 
This is due to a misunderstanding of one of the greatest 
scientific problems of our ejooch. There is not an astronomer 
who believes that the tail of a comet is a rigid whole attached 
to the nucleus : one might as well imagine that the smoke of a 
steam-boat that started from Havre, and that one sees arriving 
at New York, has crossed the Atlantic with the vessel. It is 
two centuries since Newton explained these matters by showing 
that each section of the tail taken at a given 'moment was 
* Bead before the Academy of Scieiices of Paris, July 11, 1881. 
