Paper, 'The rotation of the electric arc' by Alexander Pelham Trotter Trotter writes: 'In the course of experiments made with the view of realising as a practical standard of light, the method of using one square millimetre or other definite area of the crater of the positive carbon of an electric arc, the author has found that the effective luminosity is not as theory would predict, either constant or uniform.' Annotations in pencil and ink. Subject: Physics / Electricity Received 12 June 1894 / 15 June 1894. Communicated by Silvanus Phillips Thompson. A version of this paper was published in volume 56 of the Proceedings of the Royal Society as 'The rotation of the electric arc'. 1894