[2] In the _Quarterly Journal of Science_ for October 1866, a more detailed but somewhat less popular account of the subject of the above paper is presented. A few months earlier, a skilfully-written paper on the same subject, from the pen of Mr. J. M. Wilson, of Rugby, had appeared in the _Eagle_, a magazine written by and for members of St. John’s College, Cambridge. Although my paper in the _Quarterly Journal of Science_ was written quite independently of Mr. Wilson’s (which, however, I had read), yet it chanced that in describing the same mathematical relations, and the same sequence of events, I here and there used language closely resembling his. I fear this led for a while to some misconception; but I was fortunately able to show in Mr. De la Rue’s address to the Astronomical Society, on the same subject, passages yet more strikingly resembling some in Mr. Wilson’s paper (written subsequently and quite independently). The fact would seem to be that if two persons describe exactly the same events, and deal with exactly the same mathematical relations, it is almost certain that in more than one passage they will use somewhat similar expressions. I was actually indebted to Mr. Wilson’s paper for one illustration, however,—that derived from the movements of a supposed artificial moon; and I think that had his paper appeared in a magazine printed for general circulation, I should have referred to it. As it was, this seemed useless so far as the readers of the _Quarterly Journal of Science_ were concerned. The circumstances of the case were, indeed, far from calling for a reference; while I had in a sense made the illustration my own by detecting an important miscalculation in the original (the amount of advance being either doubled or halved—I forget which). Had I referred to Mr. Wilson’s paper, I must needs have mentioned this mistake; and it would have appeared as though I had had no other purpose in making the reference. I mention these matters to explain what I fear my esteemed fellow-collegian was disposed at the time to regard as either a wrong or a slight. Nothing was further from my intention than either. _VENUS ON THE SUN’S FACE._