6§ Royal Astronomical Societi/. 



came apprehensive that he would be unable to maintain the obser- 

 vatory, from which so much was expected, in a state of the requisite 

 efficiency. Impressed with this idea he took the resolution to give 

 in his resignation, in order that it might have the contingent benefit 

 of another appointment ; and thus an act which, hastily judged, might 

 appear to be an abandonment of his post, was the simple and natural 

 result of a high, it may be an exaggerated, sense of public duty. 

 The sacrifice involved in his resignation was of no small importance 

 to him in a pecuniary point of view ; for all he had to fall back upon 

 was a pension of 100/. a-year, to which he had become entitled upon 

 the retirement of Lord Eldin. But no one was ever less influenced 

 by considerations of personal or pecuniary advantage, and under any 

 circumstances he would have disdained the emoluments of office 

 without the most punctilious discharge of its duties. 



On his return to this country in 1833, Mr. Henderson took up his 

 abode in Edinburgh, and being now without official engagements, he 

 began the task of reducing the rich store of observations he had 

 brought with him from the Cape. The first result of this self-im- 

 posed labour Avas the determination of an important astronomical 

 element — the sun's parallax — from a comparison of observations of 

 the declinations of Mars near opposition, made at Greenwich, Cam- 

 bridge and Altona, with the corresponding observations at the Cape. 

 Previous to his departure for that station he had expressed a wish 

 that a selection should be made of such stars as could conveniently 

 be observed with Mars at the ojiposition in November 18?2, with a 

 view to the determination of the parallax, and that a list of them 

 should be circulated among diff'erent astronomers in various parts of 

 the world, for the purpose of obtaining corresponding observations. 

 Accordingly, Mr. Sheepshanks having furnished the apparent places 

 of Mars during the requisite period, and Mr. Baily having selected 

 the stars to be observed, the Council caused the list to be printed and 

 circulated with directions as to the mode in which the observations 

 should be made. In consequence of these preparations four sets of 

 corresponding observations were obtained, from each of which Mr. 

 Henderson deduced a value of the parallax. The mean of the whole 

 gave a parallax of 9""028 ; a result which is known from the more 

 certahi method of the transits of Venus to be somewhat too large, 

 as was the case also in Lacaille's attempt at the Cape in 1751, to 

 determine the solar parallax by the same method. The determina- 

 tion, he remarks, is chiefly valuable as showing the probable accuracy 

 of the method, and the limits within which this important datum in 

 physical astronomy may be determined independently of the rare 

 phsenomena of the transits of Venus. 



Another paper of a more elaborate kind followed soon after, con- 

 taining an investigation of the anomalies of the six-foot mural circle 

 in the Cape Observatory. When this instrument was first set up 

 there were found to be considersble discrepancies in the reading of 

 the diflferent microscopes, a circumstance which occasioned great 

 perplexity to Mr. Fallows ; and although that astronomer ascertained 

 that the mean of the six readings might be depended upon, he did 



