Ordinary Meeting, 2004 May 26
Henry McEwan of Glasgow
Dr McKim opened his address by introducing Dr William Sheehan, in the audience, who had created the animation of the 1882 transit of Venus shown by the previous speaker. Members expressed their appreciation of Dr Sheehan's work.
Henry McEwan, the speaker explained, had been an exceptionally active figure in the Association's history, but whose contribution was often forgotten. He was the first Director of the Mercury and Venus Section upon its foundation in 1895, and would go on to hold this post for 60 years, until his death in 1955. This made him the longest standing Section Director in the Association's history. However, despite the length of his service and the important contributions he made to the observation of these two planets, relatively little was known about his life. Living in Scotland, he was somewhat isolated from much of the Association, and his relatively limited means rarely permitted him to travel to meetings in London.
The speaker took personal interest in McEwan's life for several reasons beyond his astronomical work. Living in the Victorian era, the historical context of McEwan's contribution to the Association was markedly different from that of the present day: he was twenty years old at the time of William Gladstone's 1884 Reform Act, which extended voting rights to the working classes. The age of steam was now fully underway – a matter close to McEwan's professional training as an electrical engineer. In 1873, James Clerk Maxwell's now famous equations describing electromagnetic fields were published for the first time. Yet certain historical details were very familiar to modern astronomers – for example, McEwan's interest in amateur astronomy stemmed initially from the wonder of seeing the northern aurora.
McEwan's astronomical achievements included the publication of a highly accurate map of Mercury in 1929. He made positive observations of the Ashen Lights of Venus on several occasions. And his lifelong ambition was to measure the rotation periods of these two planets. He also made contributions to other Sections, submitting sketches of Jupiter and Mars. It was evident from these that he had fine eyesight and an excellent interpretation of colour. His diagrams for the Journal undoubtedly benefited from his professional training as an engineer. Yet McEwan never owned a large telescope – the bulk of his work was undertaken with a 5-inch refractor he bought in 1895.
He never fulfilled his aim of measuring the rotation period of Venus, though no other observers had any better luck in his lifetime. It was perhaps tantalising, given that the now-accepted rotation period of Mercury is 4.4 days, that McEwan should have identified in 1914 a curious indentation in the terminator on February 14, which reappeared on 19th. Venus proved substantially more challenging – McEwan had great difficulty in identifying any form of surface features which all observers could agree on and follow. Many observers claimed to see no surface detail at all. Observers would argue over claimed measurements of the period, but no consensus was ever reached, and none of the historical observations matched the retrograde rotation of 243-day period that is now accepted.
A more detailed account of Dr McKim's presentation can be found in the talk's accompanying paper.1 Following the applause for the speaker's thorough historical account, the President said there was no time for questions. The meeting was adjourned until Saturday June 26 at the Cavendish Laboratory, Cambridge.