324 THE WORLD MACHINE 



sun is a mere aimless flight, no whither and no whence, or 

 whether it be describing a curve about some central point. 



The surmise of a circular motion was natural. The revolu- 

 tion of the planets, the quantity of satellites which in turn 

 revolve about them possibly, for aught we know, the satellites 

 themselves may have their little moons obviously suggested 

 that this wheel-within-a-wheel arrangement is characteristic of 

 the whole cosmic order. As yet there is no evidence pointing 

 towards a central sun, but the idea that such a sun exists was 

 considerably strengthened by another of the long list of dis- 

 coveries made by this same wonderful man. 



As Bradley 's hunt for minute movements of parallax had 

 led him to the discovery of aberration, so Herschel's researches 

 in the same field led him to the discovery of the double stars. 



Galileo had long before pointed out that the stars most 

 advantageous for the discovery of a possible parallactic shift 

 are those which lie in almost identically the same line of sight. 

 The swing of the earth in its orbit would certainly produce a 

 larger and more easily detected change of position in such a 

 pair of stars than those more widely separated. Following this 

 hint, Herschel set about making a catalogue of such doublets. 

 One day the idea came that this closeness of position was not 

 a mere accident resulting from the especial angle under which 

 we see them, not a mere coincidence, as, for example, when a 

 pair of mountain peaks happen to lie in the same line of view 

 from where we are standing. The number of these coincidences 

 was far too great. Laplace and others were then engaged in 

 making the calculus of probabilities a fashionable study. The 

 simplest computation from the laws of chance sufficed to show 

 that alike the nearness and frequence of these pairs of stars 

 was far greater than would occur from any random distribution. 



So absorbing was their study that, as the difficulties of 

 establishing any angle of parallax became more and more clear, 

 Herschel gave over his attention to these perplexing appear- 

 ances. Finally his reward came. It had been for some time 

 known that the bright star which we call Castor, of the constel- 

 lation of the Twins, is in point of fact two stars, so nearly in the 

 line of sight that they appear to the eye single. From a long 

 series of observations, supplemented by another by Bradley 

 of many years before, Herschel was able to perceive a minute 

 change in the position of the two stars, such as to leave little 



