president's address. 35 



recently advanced by Mr. Lockyer. As regaixls the nebula and 

 nebulous stars, so far as we can yet speak, they seem to consist of 

 some kind of cosmical matter in a more or less heated state, for T 

 think we may take for granted that at the distances of the fixed 

 stars and nebula, no matter, even in large masses, would be 

 visible unless at a very high temperature. It may, therefore, be 

 that the objects we see are but a portion of the matter actually 

 existing. I think we may reasonably believe that in many of the 

 nebulie evolutionary changes are in progress, and we can scarcely 

 look at some of tlie planetary and disc-like nebula with bright 

 centres without imagining a condition of things such as Laplace 

 had in his mind when he devised his theory of the genesis of the 

 solar system. Although any statements of observed change in 

 the nebuhe have hitherto been regarded with considerable doubt, 

 the recent condensation in the Andromeda nebula and the 

 undoubted change that has taken place in the nebula of Eta 

 Argus since Sir J. Herschell's drawings up to the present time, 

 forces us to an admission that changes do take place, and are 

 seen readily enough to satisfy the most stubborn sceptic. The 

 relations existing between comets and meteroids, or those meteors 

 which move in regular orbits around the sun, has been a subject 

 of great interest, especially since it was found that the orbits of 

 several well-known comets were identical with those of some of 

 the meteoroids — the Leonids and Perseids, for instance. That 

 thei'e is a very intimate connection between meteoroids and 

 comets is now certain, but whether meteoroids are parts of old 

 and broken-up comets, or whether comets themselves are 

 condensed portions of tlie meteor streams, cannot yet be stated 

 with certainty. The fact that some periodic comets have become 

 smaller at successive apparitions, while others have broken up, as 

 in the case of Bella's comet, might help the former proposition. 

 The evidence of the spectroscope points to a similar constitution 

 of matter in both. 



The orbits of many of our comets, as well as some of the 

 meteor streams, extend far beyond the orbit of Neptune into the 

 apparently untenanted space between our solar system and the 

 nearest fixed stars. Does, then, the matter of which the meteors 

 and meteoroids are composed, and of which fragments are 

 constantly falling on the earth, belong only to the solar system, 

 or is it only a portion of the universal cosmical matter pervading 

 all space? These small bodies only become visible to us when 

 heated by collision either with our atmosphere or with other 

 matter or bodies of considerable density, and therefore may per- 

 vade space in almost any conceivable quantity, and yet be 

 invisible except under certain conditions. In support of such 

 a suggestion we know the metallic meteors falling to the earth 

 have hydrogen occluded within their substance, and are composed 

 of elements whose spectra are for the most part visible in many 



