56 



EEroRT — 1880. 



First and Second Reports of the Committee, consisting of Mr. David 

 Gill, Professor Gr. Forbes, Mr. Howard GtRUBb, and Mr. C. H. 

 GiMiNGHAM, appointed to consider the question of Improvements 

 in Astronomical Clocks. 



First Bepcrt. By Mr. David Gill.' 



To maintain the motion of a free pendulum in a uniform arc, when the 

 pendulum is kept in uniform pressure and temperature, and to record the 

 number of vibrations which the pendulum . performs, is to realise the 

 conditions which constitute a perfect clock. 



The conditions of absolute uniformity of impulse are, ivith one exception, 

 realised in the following arrangement. 



Let s (figs. 1, 2, 3) be the point of suspension of a pendulum, and P, 

 in the same figures, the pendulum rod. 



Fig. 1. Fig. 2. Fig. 3. 



Let w be an impulse-piece of the shape shown, suspended by a piece 

 of very delicate spring, so as to swing accurately from the same centre as 

 the pendalum. 



M is an electro-magnet, N an armature mounted on an arm A, which is 

 pivoted at Q. 



In fig. 1 the pendulum is supposed at rest ; but the armature N, and 

 the arm A are drawn, as they cannot remain, for a must either be pulled 

 against the backing pin p, by the spiral spring k, or against p2, by the 

 attraction of the electro-magnet m. 



Let us now suppose that matters are so arranged that when the im- 

 pulse-piece w acts upon the pendulum, a galvanic circuit is completed, 

 and M becomes an electro-magnet, we shall then have the position of the 

 arm A, and of the impulse arm w, as in fig. 3, and when the impulse 

 weight and pendulum rod are separated, we shall have the position of 

 these as shown in fig. 2. 



' Eead at the Sheffield Meeting, 1879, but omitted from that year's Keport at the 

 author's request. 



