188i.] on the Distances of the Fixed Stars. 95 



nearest to us — ^just as the motion of a snail could be easily watched 

 at the distance of two or three feet from the eye, but could not be 

 detected except after a long interval if the animal were a good many 

 yards distant. 



Bessel employed two faint comparison stars at right angles to 

 each other with respect to 61 Cygni, and he made two separate series 

 of observations, the first extending from August 1837 to October 1838, 

 the second from October 1838 to March 1840. 



Both series confirm each other, and the results deduced separately 

 from the measures of the two comparison stars also agree within very 

 narrow limits. From all the observations combined Bessel found the 

 parallax of 61 Cygni to be 35/100 of a second — a quantity which has 

 been shown by the modern researches of Prof. Auwers and Dr. Ball 

 to be more nearly half a second of arc. Thus at 61 Cygni the 

 diameter of the earth's orbit round the sun would appear of the same 

 size as a globe a foot in diameter viewed at 40 miles distance, or of a 

 silver threepenny-piece a mile ofi". But whilst these great masters of 

 astronomy — Struve and Bessel — had been exhausting the resources of 

 their skill in observation, and that of the astronomical workshops of 

 Europe in supplying them with the most refined instruments, a quiet 

 and earnest man had been at work at the Cape of Good Hope, and, 

 without knowing it at the time, had really made the first observations 

 which afforded strong presumptive evidence of the existence of the 

 parallax of any fixed star. 



Henderson occupied the post of Her Majesty's Astronomer at 

 the Cape of Good Hope in 1882 and 1833, and during his brief and 

 brilliant tenure of ofiice there, he made, amongst many others, a fine 

 series of meridian observations of a Centauri — a bright and other- 

 wise remarkable double star. When, after his return to England, 

 Henderson reduced these observations, and compared them with the 

 earlier observations of other astronomers, he found that a Centauri 

 had a large proper motion ; he was therefore led to examine and see 

 whether his observations gave any indication of an annual parallax. 

 He found that they did so, and not of a small parallax but of one 

 amounting to nearly a second of arc. But it was not till this was 

 confirmed, not only by the observations with the mural circle but by 

 those of the transit instrument also, not only by his own observations 

 but by those of Lieut. Meadows, his assistant, that Henderson ventured 

 to publish his remarkable result. 



In the year 1842 it was felt by the astronomical world at large 

 that the problem which hitherto had baffled astronomers had begun to 

 yield, that some approximation to the truth had at last been arrived 

 at with regard to the distance of a fixed star, and it was fit and proper 

 that the Koyal Astronomical Society of London should acknowledge 

 the labours of him who had most effectually contributed to this end. 



Henderson's results seemed sufficiently convincing, but they de- 

 pended upon determinations of the absolute place of a Centauri. 

 The experiences of the skilful astronomer Brinkley at Dublin were 

 still fresh in the minds of astronomers. He had arrived by similar, 



