That the phenomenon then had a regular connexion with the place of the earth was evident; but it was not that sort of connexion arising from the mere change of place of the earth. It is related[3] that he was led to the true explanation by observing that the vane at the top of a boat’s mast changed its direction a little whenever the boat was put about, and made to go in a contrary direction; and that on his remarking that it was curious the wind should shift every time the boat was put about, he was assured by the boatmen that the same thing always happened. Be this as it may, he proposed to the Royal Society, in 1728, his beautiful explanation of the annual motion which he had observed in the stars; namely, that it is caused by the alteration in the apparent direction of the rays of light, arising from the earth being in motion. Suppose a stream of bullets fired into a carriage in motion, in a line perpendicular to its side, and so directed as to hit the middle of the first window, but not with sufficient velocity to reach any part of the second window. It is plain that they will strike the hinder pannel, which the motion of the carriage brings forward, and that to passengers in the inside the direction of the stream will appear to be from the middle of the window at which it enters to the opposite hinder pannel: whereas, had the carriage been at rest, it would have appeared to pass through the centre of both windows. And to make the stream really pass through both windows it must, if the carriage be in motion, be directed through the nearer window towards the foremost pannel on the other side. A ray of light is in the same situation with regard to the spectator, both as to the diurnal and the annual motion of the earth. The former gives an insensible aberration only; the latter, one which though small is sensible. The smallness of the latter aberration arises from the velocity of light being more than ten thousand times that of the earth in its orbit. And it must be remembered that the motion of light was not an hypothesis, invented to form the basis of Bradley’s explanation, but was ascertained before his time, by Römer, from a phenomenon of an entirely different nature; namely, the retardation observed in the eclipses of Jupiter’s satellites, as the planet moved from the earth. The absolute deduction of the laws of aberration was completed by Bradley. Footnote 3: Professor Rigaud gives this story on the authority of ‘Dr. Thomson’s History of the Royal Society,’ in which work we find no authority cited for it. We cannot find it in any other place, but are credibly informed that it rests on good traditional evidence.