know the size of the orbits, and we know the time in which the revolutions are accomplished. It is the mathematician who enables the mass of the bodies to be determined, and the result is not a little astonishing. It tells us that the mass of the two component stars which form the primary of Mizar is not less than forty times as great as the mass of the sun. Here is indeed a result equally striking on account of the method by which it is obtained and of the startling character of the conception to which it leads.
Remember that in all this the distance of the star from the earth is not concerned, for the results at which we have arrived are absolutely independent of the distance at which the star may happen to be placed. We already knew the masses of some few binary stars by the application of the older process, but in all such cases it was necessary that we should have a previous knowledge of the star's distance. This is always a precarious element, and in the majority of cases it is wholly out of our power to discover it. Now, however, we are entitled to expect large additions to our knowledge of the stars, their masses, and their movements, notwithstanding the fact that the distances may be too vast to be appreciated by any means at our disposal.
The instances that have been given will suffice to show the versatility of the new method. It is the alliance of photography with spectroscopy that makes the present time so full of promise. Already the orbits of 150 Stars have been determined by the beautiful spectroscopic process.
