28 SOME NEW DOUBLE STARS AND SOUTHERN BINARIES. 
between them, so that this seems to be a well marked instance of 
this curious phenomenon, viz., two immense bodies revolving about 
a point in space, 7.¢., about nothing ; but this implies more, for while 
one star appears to us to be going round the other, both would, if we 
could refer their position to some fixed point, be found to have 
changed their places in proportion to their motion in their orbits. It 
so happens that these stars are now favourably situated for detecting 
such a change with the transit instrument, and they will be regularly 
observed for that purpose. But from an examination of the Cape 
adras catalogue it seems evident that the star taken as the 
fixed one is actually in motion. But the question may be viewed 
in another way ; unless stars are connected in binary systems, the 
only test we have of their magnitude is the amount of light they 
send to us. Now, here we have two stars equal in light and there 
fore theoretically equal in size, and, as we have seen before, 
all the observations go to show that if this is a binary the apparent 
orbit is an ellipse of which one star does not occupy the centre — 
and therefore, though equal in brilliance, one must be larger than 
the other. a 
It was my intention to have placed before you facts relatimg 
to several other southern binary stars, but the pressure of other — 
engagements has rendered this impossible now, but I hope at 20 
distant date to place before you some of the results of my observ 
tions of Sir John Herschel’s doubles, and I may then include 
information I am now obliged to defer. I may say, however, 4 
the number of those which give certain evidence of being bmary 
