1. Herschel to Aubert, 9 January 1782, Royal Astronomical Society MS Herschel W.1/1, pp. 21-22
2. Lubbock C. A., The Herschel chronicle (Cambridge, 1933), hereafter cited as Chronicle, 102-3.
3. RAS MS Herschel W.1/5.1; Chronicle, 64–65. Herschel would have derived the notion of light-gathering power from Robert Smith's Opticks, see Hoskin M. A., William Herschel and the construction of the heavens (London, 1963), 21.