Paper, 'On a new form of Air Leyden, with application to the measurement of small electrostatic capacities' by Lord Kelvin [William Thomson] Thomson writes: 'In the title of this paper as originally offered for communication “Air Condenser” stood in place of “Air Leyden" but it was accompanied by a request to the Secretaries to help me to a better designation than “Air Condenser” (with its ambiguous suggestion of an apparatus for condensing air), and I was happily answered by Lord Rayleigh with a proposal to use the word “leyden” to denote a generalised Leyden jar, which I have gladly adopted. The apparatus to be described affords, in conjunction with a suitable electrometer, a convenient means of quickly measuring small electrostatic capacities, such as those of short lengths of cable.' Annotations in pencil and ink. Includes notes to the printer. Subject: Scientific apparatus and instruments Received 31 May 1892. Read 2 June 1892. A version of this paper was published in volume 52 of the Proceedings of the Royal Society as 'On a new form of Air Leyden, with application to the measurement of small electrostatic capacities'. 1892