37S T. C. CHAM BERLIN 



hii^lilv erratic orbits is irwnincut, and these are specially subject to sttll 

 further cJianges, and tints these fragmental clusters come to possess by 

 the very circumstances of their birth the second characteristic of comets, 

 as zvell as the first. 



Whether they would possess at the same time, or come at 

 length to possess, the third characteristic of comets, the attenu- 

 ated matter of which cometic tails are made, is not so clear, 

 since the nature of this matter and its condition are not yet fully 

 known. The recent discoveries relative to the extreme ionization 

 of matter and perhaps even its corpuscular dissociation, and the 

 radio-activity of certain kinds of matter are at least very sugges- 

 tive in this connection. Six of the elements reported by good 

 authority as detected in meteorites, are known to possess, or to 

 be habitually associated with, radio-active matter, viz., barium, 

 bismuth, cerium, lead, titanium, and uranium. It is not very 

 material here whether this radio-activity is really possessed by 

 all these elements themselves, or simply by substances associated 

 with them. If the coma and tails of comets are dependent 

 on rare substances of a radio-active or extremely volatile nature, 

 and hence permanently retensible only in the interior of bodies, 

 it would be difficult to imagine conditions more favorable for 

 setting them free in unusual volume than minute tidal disruption ; 

 particularly is this true if the retention of these substances is 

 dependent on low temperature, as seems to be the case, since 

 they are brought forth and driven away at a highly accelerated 

 rate as the sun is approached. This view seems also to be sup- 

 ported by the fact that comets which remain long in the vicinity 

 of the sun, as for example the short-period comets, lose their 

 tails in a brief period. ' 



If the attenuated cometic matter owes its essential peculiarities 

 to electric states, these might perhaps be derivable from the 

 revolutionary movements of the magnetic elements in the frag- 

 mental swarm, for by the hypothesis of tidal disruption the 

 swarm should inherit a rotatory movement, and the fragments 

 should contain both magnetic and magnetizable matter, variousl}' 

 associated with diamagnetic matter. 



