Royal Ash'onomical Society. l^Q 



the contact of the rod with which produces the friction that prevents 

 further acceleration, the Astronomer Royal proposes the following 

 simple construction. The ring is to he of brass, and is to be car- 

 ried in two or more points of its circumference by horizontal bars, 

 each bar being supported at the extremity furthest from the ring by 

 an iron pillar, and at some point between the iron pillar and the ring 

 by a brass pillar ; the pendulum rod and all other parts of the frame 

 being of iron. The expansion of the brass ring, and its elevation by 

 the effect of the different expansion of the two pillars carrying each 

 horizontal bar, will both contribute (and may be made to do so to 

 any assignable degeee) to permit the greater angular expansion of 

 the conical motion which is necessary for isochronism when the pen- 

 dulum rod is lengthened by heat. [It is well known that the time 

 of rotation of the conical pendulum depends only on the vertical de- 

 pression of the ball below the horizontal plane passing through the 

 centre of motion.] 



It may, however, be thought preferable to employ a mercurial 

 pendulum of the ordinary construction as regards compensation, 

 revolving in a very small circle, whose diameter is perhaps equal to 

 the usual arc of vibration of a common clock pendulum, and whose 

 dimensions are limited only by the resistance of the air. The radial 

 arm ought to act on a slender spike at the bottom of the mercury- 

 cistern. The pulling- weight would be very light, but the efficiency 

 of the regulation would not be diminished by that circumstance. 

 No ring would be necessary, except as a safety-guard, to prevent 

 the machinery from running wild on any accidental excursion of 

 the pendulum beyond the end of the radial arm. 



The Astronomer Royal then remarked that, considering the pro- 

 blem of smooth and accurate motion as being now much nearer to 

 its solution than it had formerly been, it might be a question whether, 

 supposing a sidereal clock made on these principles to be mounted 

 at the Royal Observatory, it should be used in communicating 

 motion to a solar clock. It might by some persons be thought ad- 

 vantageous, even now, that the drop of the signal-ball (at 1** Green- 

 wich mean solar time) should be effected by clock-machinery ; and 

 it is quite within possibility that a time-signal may be sent from the 

 Royal Observatory to different parts of the kingdom at certain mean 

 solar hours every day, by a galvanic current regulated by clock-ma- 

 chinery. Whether it would be advisable that this should be done 

 by machinery proceeding originally from the sidereal mover, would 

 be a question for consideration at the proper time ; but, at all events, 

 the Astronomer Royal desired to show that the problem is practi- 

 cally possible to an astonishing degree of accuracy. Dr. Henderson, 

 of Newferry near Birkenhead, had communicated to the Astronomer 

 Royal, and had permitted him to make known to the Society, the 

 following numbers for the teeth of wheels. If there be three spin- 

 dles, Nos. 1, 2 and 3, No. 1 revolving in a mean solar day of 24 

 hours, or 86,400 solar seconds, and if No. 1 carries a wheel of 247 

 teeth working in a wheel of 331 teeth on No. 2, and if No. 2 also 

 carries a wheel of 43 teeth working in a wheel of 32 teeth on No. 3, 

 then No. 3 ^YilI revolve in 23^^ oe"™ 4«-09001. Again, if there be 



