Paper, 'On certain geometrical theorems, No. 1' by W H L [William Henry Leighton] Russell Russell presents a proof of the equation to a circle inscribed in a triangle, expressed in trilinear co-ordinates. Annotations in ink. Includes two geometrical diagrams and a note from William Spottiswoode. Subject: Mathematics / Coordinate geometry Received 12 November 1881. Read 22 December 1881. A version of this paper was published in volume 33 of the Proceedings of the Royal Society as 'On certain geometrical theorems. No. 1'. 1881