But the greatest extension of our knowledge of stellar distances, in recent years, is due to a Scottish astronomer, who has maintained the reputation of Scotland, and also of the Cape Observatory, in this line of research. Born in Aberdeen in 1843, _David Gill_ directed Lord Lindsay’s private observatory at Dunecht, in Aberdeenshire, from 1876 to 1879. In the latter year he succeeded _Edward James Stone_ (1831-1897) as Astronomer-Royal at the Cape, a position which he has since filled with conspicuous ability. From 1881 he has been engaged in the hunt for parallax. In conjunction with _William Lewis Elkin_ (born 1855), now director of Yale College Observatory, he determined the parallaxes of nine stars with the aid of Lord Lindsay’s heliometer. In 1887, with a larger instrument, he resumed the search, while Elkin worked in co-operation with him, but at Yale Observatory, where he undertook the measurement of the parallaxes of northern stars. He fixed in 1888 an average parallax for first-magnitude stars, which was determined at 0·089″, corresponding to a journey for light of thirty-six years. Most of the successful determinations of parallax have been made by the “relative” method—that is, the determination of the displacement of a star in reference to another star, assumed to be situated at an immeasurable distance. The method of absolute parallax, on the other hand,—the star’s displacement in right ascension and declination,—has been seldom used, owing to the laborious reduction which has to be gone through before the result can be reached. In 1885, however, a series of observations were undertaken at Leyden by _Jacobus Cornelius Kapteyn_ (born 1851), who determined by the absolute method the parallaxes of fifteen northern stars. The first application of photography to the problem was due to the zeal and energy of _Charles Pritchard_ (1808-1893), Professor of Astronomy at Oxford, who determined by this method the parallax of 61 Cygni, which he announced in 1886 to be 0·438″, in agreement with Ball’s determination. He also determined the average parallax of second-magnitude stars, which came out as 0·056″. Since the time of Pritchard’s observations various other more or less satisfactory determinations of parallax have been made. Few of the parallax determinations are probably very accurate, and none exact; but an idea of the difficulty of the measurement may be gathered from the remark of an American writer, Mr G. P. Serviss, that the displacement “is about equal to the apparent distance between the heads of two pins, placed an inch apart, and viewed from a distance of a hundred and eighty miles.”