In reply to Tycho, it was said that, since the parallax of a body diminishes as its distance increases, a star may be so far off that its parallax may be imperceptible.  This answer proved to be correct.  The detection of the parallax of the stars depended on the improvement of instruments for the measurement of angles.

The parallax of alpha Centauri, a fine double star of the Southern Hemisphere, at present considered to be the nearest of the fixed stars, was first determined by Henderson and Maclear at the Cape of Good Hope in 1832-’33.  It is about nine-tenths of a second.  Hence this star is almost two hundred and thirty thousand times as far from us as the sun.  Seen from it, if the sun were even large enough to fill the whole orbit of the earth, or one hundred and eighty million miles in diameter, he would be a mere point.  With its companion, it revolves round their common centre of gravity in eighty-one years, and hence it would seem that their conjoint mass is less than that of the sun.

The star 61 Cygni is of the sixth magnitude.  Its parallax was first found by Bessel in 1838, and is about one-third of a second.  The distance from us is, therefore, much more than five hundred thousand times that of the sun.  With its companion, it revolves round their common centre of gravity in five hundred and twenty years.  Their conjoint weight is about one-third that of the sun.

There is reason to believe that the great star Sirius, the brightest in the heavens, is about six times as far off as alpha Centauri.  His probable diameter is twelve million miles, and the light he emits two hundred times more brilliant than that of the sun.  Yet, even through the telescope, he has no measurable diameter; be looks merely like a very bright spark.

The stars, then, differ not merely in visible magnitude, but also in actual size.  As the spectroscope shows, they differ greatly in chemical and physical constitution.  That instrument is also revealing to us the duration of the life of a star, through changes in the refrangibility of the emitted light.  Though, as we have seen, the nearest to us is at an enormous and all but immeasurable distance, this is but the first step—­there are others the rays of which have taken thousands, perhaps millions, of years to reach us!  The limits of our own system are far beyond the range of our greatest telescopes; what, then, shall we say of other systems beyond?  Worlds are scattered like dust in the abysses in space.

Have these gigantic bodies—­myriads of which are placed at so vast a distance that our unassisted eyes cannot perceive them—­have these no other purpose than that assigned by theologians, to give light to us?  Does not their enormous size demonstrate that, as they are centres of force, so they must be centres of motion—­ suns for other systems of worlds?