Caroline Lucretia Herschel, Philosophical Transactions of the Royal Society… (1787)
“ August 2. 10 h. 9′, the comet is now, with respect to the stars a and b*, situated as in fig, 4, therefore the motion since last night is evident.10 h. 30′, another considerable star c may be taken into the field with it, by placing a in the center; when the comet and the other star will both appear in the circumference, as in fig. 5, These observations were made with a Newtonian sweeper of 27 inches focal length, and a power of about 20, the field of view is 2° 12′. I cannot find the stars a and c in any catalogue; but suppose they may easily be traced in the heavens ”
