54 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



that they must have been formed under conditions very 

 different from those which prevail on the earth's sur- 

 face. I may mention, for instance, the peculiar form of 

 crystallised silica, called by Maskelyne, Asmanite ; and 

 the whole class of meteorites, consisting of iron gene- 

 rally alloyed with nickel, which Daubre*e terms Holo- 

 siderites. The interesting discovery, however, by 

 Nordenskiold, in 1870, at Ovifak, of a number of blocks 

 of iron alloyed with nickel and cobalt, in connection 

 with basalts containing disseminated iron, has, in the 

 words of Judd, ' afforded a very important link, placing 

 the terrestrial and extra-terrestrial rocks in closer rela- 

 tions with one another.' 



We have as yet no sufficient evidence to justify a 

 conclusion as to whether any substances exist in the 

 heavenly bodies which do not occur in our earth, though 

 there are many lines which cannot yet be satisfactorily 

 referred to any terrestrial element. On the other hand, 

 some substances which occur on our earth have not yet 

 been detected in the sun's atmosphere. 



Such discoveries as these seemed, not long ago, 

 entirely beyond our hopes. M. Comte, indeed, in his 

 ' Cours de Philosophic Positive,' as recently as 1842, 

 laid it down as an axiom regarding the heavenly bodies, 

 that ' Nous concevons la possibilite de determiner leurs 

 formes, leurs distances, leurs grandeurs et leurs mouve- 

 ments, tandis que nous ne saurions jamais e*tudier par 

 oucun moyen leur composition chimique ou leur struc- 

 ture mine'ralogique.' Yet within a few years this 

 supposed impossibility has been actually accomplished, 

 showing how unsafe it is to limit the possibilities of 

 science. 



