140 Royal Society. 



observatory, every room may be furnished with an instrument, sim- 

 ple in its construction, and therefore little liable to derangement, and 

 of trifling cost, which shall indicate the time, and beat dead seconds 

 audiblj% with the same precision as tlie standard astronomical clock 

 with which it is connected ; thus obviating the necessity of having 

 several clocks, and diminishing the trouble of winding up and regu- 

 lating them separately. In like manner, in public offices and large 

 establishments, one good clock will serve the purpose of indicating 

 the precise time in every part of the building where it may be re- 

 quired, and an accuracy ensured which it would be difficult to obtain 

 by independent clocks, even putting the difference of cost out of 

 consideration. Other cases in which the invention might be ad- 

 vantageously employed were also mentioned. In the electro-mag- 

 netic clock, which was exhibited in action in the Apartments of the 

 Society, all the parts employed in a clock for maintaining and regu- 

 lating the power are entirely dispensed with. It consists simply of 

 a face with its second, minute and hour hands, and of a train of 

 wheels which communicate motion from the arbor of the second's 

 hand to that of the hour hand, in the same manner as in an ordinary 

 clock train ; a small electro-magnet is caused to act upon a pecu- 

 liarly constructed wheel (scarcely capable of being described without 

 a figure) placed on the second's arbor, in such manner that whenever 

 the temporary magnetism is either produced or destroyed, the wheel, 

 and consequently the second's hand, advances a sixtieth part of its 

 revolution. It is obvious, then, that if an electric current can be al- 

 ternately established and arrested, each resumption and cessation 

 lasting for a second, the instrument now described, although unpro- 

 vided with any internal maintaining or regulating power, would per- 

 form all the usual functions of a perfect clock. The manner in which 

 hi s apparatus is applied to the clocks, so that the movements of the 

 hands of both may be perfectly simultaneous, is the following. On 

 the axis which carries the scape-wheel of the primary clock a small 

 disc of brass is fixed, which is first divided on its circumference into 

 sixty equal parts ; each alternate division is then cut out and filled 

 with a piece of wood, so that the circumference consists of thirty 

 regular alternations of wood and metal. An extremely light brass 

 spring, which is screwed to a block of ivory or hard wood, and which 

 has no connexion with the metallic parts of the clock, rests by its 

 free end on the circumference of the disc. A copper wire is fastened 

 to the fixed end of the spring, and proceeds to one end of the wire 

 of the electro-magnet; while another wire attached to the clock-frame 

 is continued until it joins the other end of that of the same electro- 

 magnet. A constant voltaic battery, consisting of a few elements 

 of very small dimensions, is interposed in any part of the circuit. 

 By this arrangement the circuit is periodically made and broken, in 

 consequence of the spring resting for one second on a metal division, 

 and the next second on a wooden division. The circuit may be ex- 

 tended to any length ; and any number of electro-magnetic instru- 

 ments may be thus brought into sympathetic action with the standard 

 clock. It is only necessary to observe, that the force of the battery 



