BLECTRO-JIAO.VETIC CLOCKS.] UNDULATORY FORCES. ELECTRO-MAGNETISM. 



253 



each other. The electric current is successively ad- 

 mitted to each electro-magnet, commencing with the top 

 one. This pulls one plate down, and so moves the crank- 

 shaft a little : each electro-magnet does the same to its 

 super-imposed plate ; and so the crank is gradually 

 moved. Five series of these arrangements are placed 

 side by side ; and, by their successive action, a rotatory 

 motion of a shaft is produced. Each plate has to move 

 not more than an eighth of an inch, and is, therefore, 

 always in close proximity to the electro-magnet beneath 

 it. As soon as these have done their portion of the 

 work, the current is cut off and directed to the neigh- 

 bouring series. One of these machines produces a con- 



rig. 16. 



siderable amount of force, 

 and, in our opinion, is a 

 decided improvement on 

 their predecessors. Fig. 

 1C will give an idea of 

 Mr. Allan's arrangement ; 

 but we have only shown 

 one frame out of four or 

 five, which are placed 

 side by side, and con- 

 nected with one crank- 

 shaft. Mr. Allan also 

 uses five sets of electro- i is 

 magnets instead of three 

 at least, so his model 

 which was deposited iii 

 the London Polytech- 

 nic, was constructed : 

 a a a are three electro- 

 magnets, firmly fixed in 



i -'' a frame ; &', 6', and 6, are 



three soft iron circular 



plates, loosely resting on pins, which are fixed on the 

 vertical rod, c. It will be observed, that each plate 

 varies in the distance from its electro-magnet. The 

 rod c is attracted at d to another, e, which again is con- 

 nected with the crank /, fixed on the shaft g. M h, n .1 

 current of electricity is sent round each electro-magnet 

 successively, they attract, one after another, the plates 

 over them, and so, by a succession of pulls, produce a 

 rotary motion. In this, as in every other electro-motive 

 machine, the residual magnetism* is a constant source 

 of difficulty; and if a powerful battery be employed, 

 some of the plates become fixed to their subjacent 

 electro-magnets, after the current has been cut off. The 

 mode of breaking contact we have not shown : it is, 

 however, extremely simple cutting off the current from 

 each electro-magnet with great precision. 



Ilaving thus endeavoured to acquaint our readers 

 with the principles on which electro-magnetic machines 

 are constructed, we shall dismiss the subject, with an 

 expression of regret, that so little success has, as yet, 

 rewarded the efforts of those who have devoted their 

 attention to it. 



ELECTRO- MAON-ETIC CLOCKS. Numerous attempts 

 have been made to accommodate clockwork to the 

 arrangements which afford electric and induced magnetic 

 currents. These inventions have, in almost all cases, 

 proved to be failures. Such, however, have not l>een 

 owing to a fault in the principle, so much as the defects 

 which occurred in the practical details. We need scarcely 

 say that electro-magnetism supplies a power which is 

 constant so long as a voltaic battery gives what we may 

 term the initiative ; but it is not simply on the electric 

 current that the success of the clock arrangement de- 

 jienrls. There are many other details which interfere ; 

 and although minor in their character, their effect is 

 none the less felt. For instance, we will presume the 

 case of a clock of the highest class of manufacture, which 

 has the necessary arrangements for carrying out the 

 purpose to which we have referred; that is, the indica- 

 tion of exact meridional time at any place within reach, 

 by means of conducting wires of an electro-voltaic 

 current. Such an instrument will only afford accurate 

 indications of time so long as the wheel, which is ordi- 



See antr, pp. 249 and 251. 



narily connected with the detent of the pendulum, 

 vibrates or passes any fixed point on the clock-face, 

 corresponding to the original whence it first obtained its 

 motive power. Now, this is carried out by means of a 

 wheel, the spokes of which are alternately made of a con- 

 ductor and non-conductor. A current of electricity is con- 

 veyed to the wheel; and from it is stretched a wire, 

 which reaches a similar wheel in a distant clock. Another 

 wire from this or an earth-current arrangement (which 

 we shall describe hereafter) is also employed, so that the 

 current from a battery may circulate completely between 

 the two clocks. Each clock is furnished with an electro- 

 magnet ; and as a current passes from one to the other, 

 it simultaneously sets each magnet in action. By so 

 doing, a detent acts on the usual clockwork arrangement, 

 just in a similar manner as is observed in the arrange- 

 ment of the pendulum and first wheel of the common 

 clock. Now, supposing there are sixty alternate con- 

 ductors on the wheel of the first or primary clock, it 

 is evident, that as each of these sends a current of 

 electricity to the distant clock, its electro-magnet will 

 be acted on, and its mechanism will be put in motion. 

 Each minute is thus indicated on the clock-face by a 

 movement of the minute-hand, which corresponds with 

 that of the wheel moved by the electro-magnet. It 

 also evident that any number of clocks may be 

 similarly worked by one primary; and so exact time 

 could bo indicated at any station distant from a cen- 

 tral point. 



This, however, whilst appearing perfectly easy on 

 paper, is a very different affair in practice. It was pro- 

 posed thus to regulate all the clocks on the railways of 

 the United Kingdom, by an extension of wire from a 

 central clock at Greenwich Observatory. This was, in 

 part, carried into practice at the telegraph station at 

 Charing-cross, London. Like many preceding attempts, 

 however, it failed. In the folio plate, Figs. 1 anil L> will 

 give a general idea of the construction of electro- magnetic 

 clocks. Tlie arrangement of vibrating levers, electro-mag- 

 nets, detents, toothed-wheels, connecting wires, etc., will 

 easily be understood, in connection with the above re- 

 marks. In our future pages, we shall refer to other in- 

 ventions, which will be better included with the telegraph, 

 the electric time-ball, itc. 



SECONDARY INDUCTION THE COIL 

 MACHINE. 



IN all the instruments we have hitherto described in 

 connection with electro-magnetism, we have merely 

 noticed the magnetic effect which is produced when a 

 current of electricity is conveyed by a wire. We shall 

 now investigate a different class of phenomena, in which 

 a second current of electricity is induced by tho primary 

 current in any wire near to, but not in contact with, 

 that attached to a voltaic battery. 



For the purpose of trying the experiments wo shall 

 introduce, the reader will require two or three cells of 

 any form of voltaic battery, and a supply of covered 

 copper wire, of two sizes namely, No. 16 and 22, or 

 a finer gauge; and, to prevent circumlocution, we m.ay 

 here state, that when we employ the term primary to a 

 wire, wo mean that which conveys tho current of elec- 

 ;ricity from the battery ; and tho secondary wire, is that 

 in which a current is induced by its proximity to the 

 primary one. Electro-magnetic induction is analogous 

 ;o that of frictional electricity ; but differs from it in one 

 respect namely, that the two phases of electrical con- 

 ditions are simultaneously produced by the first inducing 

 cause. Thus, if any glass surface bo charged with fric- 

 tional electricity, t its opposite side assumes one opposite 

 electrical state only; but when a wire suffers electro- 

 magnetic, or secondary induction, one of its ends ex- 

 libits a positive, and the other a negative electrical 

 state ; and, so far, this phenomenon much resembles that 

 of ordinary magnetic induction. There is, however, this 

 xsculiarity about that of electro-magnetism which is, 

 ;hat it is instantaneous in its existence ; and occurs, in 

 t See nntfj p. 180. 



