24 J. MORlSON : ADDRESS — 



many important respects. Most of them seem to be of less 

 density and give out more light in proportion to their mass 

 than the Sun does. Professor Newcombe says in his book on 

 ' The Stars ' : " The stars in general are not models of our Sim, 

 but have a much smaller mass in proportion to the light they 

 give than the Sun has. They must therefore have either a less 

 density or a greater surface-brilliancy." And again : " We must 

 conclude that at least the brighter stars are in general composed 

 of matter much less dense than that of the Sun. Many of them 

 are probably even less dense than air, and in nearly all cases the 

 density is far less than that of any known liquid." Most of 

 them would therefore seem to be in an earlier stage of develop- 

 ment. But the reverse is the case with a certain number of the 

 less brilliant stars, some of which are more massive in proportion 

 to their light than the Sun is. 



A very large number of the stars are not single like our Sun, 

 but double ; that is, composed of two bodies revolving round 

 each other, or rather round a common centre. These two bodies 

 may be nearly equal, or they may differ very much either in size or 

 in brilliancy or in both. Sometimes the more massive component 

 is the more brilliant, but quite as frequently the reverse is the 

 case. Sometimes the components of a double star are com- 

 paratively far apart, and travel in orbits which may take as long 

 as 300 or 400 years to traverse, and in other cases they are so 

 close together as almost actually to touch, and revolve round 

 each other in a few days or even hours. These close doubles 

 appear to be in an early stage of development, and in many 

 cases their mass is very small in proportion to their luminosity. 

 In one instance the mean density of the two bodies has been 

 stated to be no greater than that of our atmosphere. Double 

 stars are very common : in fact, it has been said that the great 

 majority of the stars are double. 



There are also triple stars, quadruple stars, multiple stars. In 

 some of these cases of multiple stars it has been shown that the 

 bright stars are associated with dark bodies, sometimes of much 

 greater mass than their lucial companions. Thus the existence 

 of dark stars is proved. In such cases we have a sort of reversed 

 Solar System with a large dark body in the centre, and small 

 bright secondary orbs circulating round it. We may conceive 

 the mode of formation of double stars to be as follows : — a very 

 tenuous fluid mass, rotating on its axis very rapidly, becomes 

 disrupted or split into two parts, which continue rotating roimd 

 each other, at first in close proximity ; then as time goes on the 



