10 PRESIDENTIAL ADDRESS. 
tory. But these would be speculations which could not, at 
present, be verified, and so we must content ourselves with 
the chondroi as the earliest form of matter known to us. 
Through the action of gravitation much of the cosmic dusi _ 
is supposed to have aggregated into meteorites. whose irregu- 
lar movements were, in certain places, reduced to order; 
and so arose a number of meteoritic streams, or swarms. 
moving through space. Still, under the force of cravitation, 
each of these swarms got more and more dense, until, at 
last, collisions took place between the meteorites; light and 
heat were given out, and the swarm became a nebula. The 
heat produced by the collisions would, at first, be slight, but 
would gradually increase, until the whole of the solid 
material was resolved into vapour, and a star was formed. 
Concentration, however, would still go on, and the tempera- 
ture of the star would rise, until, in time, the loss by radia- 
tion more than counterbalanced the gain by concentration, 
when the star would begin to cool. At last light would nu 
longer be given off, and the star would end by becoming a 
dark cold body moving in space. Of course, some stars 
would attain a higher maximum temperature than others, 
and either a single or a double star might be the result of the 
condensation ; but all would follow a somewhat similar de- 
velopment. 
Now, as a matter of fact, the spectroscope shows us that 
stars in all these stages actually exist at the present day in 
the heavens. In some the temperature is increasing, in 
others it is decreasing; and, although small stars must run 
through their development quicker than large ones, this is 
quite insufficient to account for all the present differences. 
From which it follows that some of the stars are much older 
than others. The sun was amongst the earliest of formed 
stars. | When it was born the sky must have presented an 
almost uniform blackness. There was no Milky-Way; no 
Orion nor Southern Cross; no Pleiades nor Dog-star. AH 
these, and many others, have been added since; not alto 
gether, but one after the other, through the long ages during 
which the sun was undergoing development. Judging by 
the relative ages of the stars, it seems probable that the pro- 
cess of concentration of the original cosmic dust commenced 
near the Solar System, and spread outwards to the Milky- 
Way. But, however this may be, the process is not yet 
over. Many nebule have not yet condensed into stars. 
Swarms of meteorites still traverse space, and, even in the 
neighbourhood of the Solar System, they are so abundant 
that the earth alone is estimated to collect more than twenty 
millions each day. 
