HENDERSON, THOMAS, was the son of a respectable tradesman at Dundee, where ho was born December 28, 1798. After au educa tion such as hia native town could afford, he VMS apprenticed to a writer (or attorney) for six years. At the end of this term ho was sent to Edinburgh, at the age of tiveuty-one, to complete his legal instruction. He was then successively secretary to the celobrated judge John Clerk of Eldiu, the Earl of Lauderdale, and the Lord Advocate Jeffrey, and in these employments ho continued till 1331.
During his reeideneo at Dundee, Henderson acquired a taste for practical astronomy, as well as for the history and literature of that science. At Edinburgh he frequented the observatory, then a very small establishment, but sufficiently well equipped to give valuable opportunities to a learner. Weak health and a tendency to disorder in the eyes are very poor aide to an astronomer, but they did not hinder 11r. Henderson from bringing himself into notice, though his acieutitio pursuits could only be the relaxations of a life of business. In 1821 he began to communicate with Dr. Thomas Young, then superinteudeut of the ' Nautical Almanac,' whom he assisted both by methods and calculations. The consequence was, that at Young's death it was found that he had placed in the hands of Professor Itigaud a memorandum desiring that the Admiralty might be im mediately informed, as soon as his death should take place, that he knew of no ono more competent than Mr. Henderson to be appointed his successor. The government however confided the trust to Mr. Pond, the astronomer royal, who immediately offered Mr. Henderson, on terms of remuneration, employment for a great part of his time. This offer was not accepted : but on the death of Mr. Fellows the Admiralty proposed to Mr. Henderson to succeed him in the charge of the observatory at the Cape of Good Hope. This offer was accepted; and from April 1832, the date of his arrival at the Cape, he must be considered as a professional astronomer.
After vigorous application to his duties fur little more than a year, he found his health and spirits give way. His isolated position and separation from his family, accompanied by the knowledge that he was subject to a disorder of the heart, which might at any time, and which finally did, prove fatal, made him wish to return to Scotland. He came back accordingly in 1833, with a rich store of observations, the reduction of which he imposed upon himself as a voluntary duty. In 1834, by an agreement between the government and the Astro nomical Institution of Edinburgh, the latter gave up their observatory to the university, the government agreeing to appoint and provide for an astronomer, who was also to hold the professorship of practical astronomy in the university. On the recommendation of the Aetro. nomical Society of London, to whom Lord Melbourne applied for advice, Mr. Henderson was appointed the first astronomer royal for Scotland. Here, in the midst of his friends, and in the position
which, of all that could have been imagined, he would have chosen for himself, he pursued his observations and researches till his death, which took place suddenly, November 23, 1844.
A very full account of Mr. Henderson's astronomical writings will be found in the Annual Report of the Astronomical Society for 1845, with a list of his writings, which consist of upwards of seventy com munications, of different degrees of magnitude and importance, to different scientific publications, independently of the volumes of observations which issued from the Edinburgh Observatory. We might particularise what he did on occultations, on the solar and lunar parallaxes, but it will better suit our limits and the nature of the subjects, to refer the reader to the memoir just cited, and to confine ourselves to a mention of the manner in which his name is connected with the discovery of the parallax of the fixed stars. Mr. Henderson, when at the Cape, repeated the attempt in which Brinkley had failed, namely, the detection of the effect of parallax upon the meridian observations. The stare chosen were at and css Centauri ; and the results derived from the former star show discordances, both in right ascension and declination, very much resembling those which parallax would cause. Mr. Main, in his elaborate investigation of the modern claims upon this subject (I Mem. Astron. Soc.,' vol. xii.) says that in the event of a parallax at all comparable to that assigned by Mr. Henderson being ultimately found to belong to the star, he will deserve the merit of the first discovery. Mr. Maclear, Mr. Henderson's successor, made a new series of observations on the same stars, with a different instrument, from which Mr. Henderson produced results very nearly agreeing with his own.
The private character and social qualities of Mr. Henderson are among the pleasant recollections of those who knew him. In his astronomical career he resembled his friend Mr. Baily in bringing to his subject the most methodical habits of business. He was well acquainted with astronomical literature, and with other branches of science; and at different times supplied the places of the professors of mathematics and of natural philosophy in the University of Edin burgh. He formed a great attachment to the methods of the German astronomers, and his models were MM. Hemel and Struve. His deter mination to be well acquainted with all that was doing abroad made him collect an astronomical library which, for a man of his very limited Means, was of extraordinary extent and goodness ; and those who knew him remember the ready manner in which ho could produce the results of his reading. Of his writings we may say briefly that, in addition to their valuable masses of observations, they abound in all that distinguishes the astronomer, properly so called, from the noter of phenomena.