30 Lord Kayleigh on Huygens's Gearing in 



usually, as shown by Mr. Enright, electrically charged (§ 4). 

 So far as these present experiments show, no electrification is 

 produced by simple effervescence unaccompanied by chemical 

 change (§ 17). 



The sign of the electrification is influenced by the kind of 

 chemical or voltaic action taking place, and is apparently not 

 due to any " contact effect" (§§ 4 to 11). 



When the effluvium is that given off from zinc dissolving 

 in hydrochloric acid (taken as a typical experiment), and 

 consists of hydrogen accompanied by foggy matter, it is not 

 decided whether the charge is given originally to the gas or 

 the fog particles, though the balance of evidence inclines 

 perhaps towards the latter view (§§ 12 to 16). The fog in 

 question is formed apparently at, or nearly at, the same 

 time and place as the gas (§ 12) ; and the nature of its 

 charge (if any) is therefore possibly influenced by the voltaic 

 conditions there present. 



The gas, or effluvium, from the decomposition of a liquid 

 by a current from the poles of a separate battery immersed in 

 it (voltameter) appears also to be electrified (§ 19). 



Belfast, April, 1890. 



III. On Huygens's Gearing in illustration of the Induction 

 of .Electric Currents. By Lord Bayleigh, Sec. R.S., Pro- 

 fessor of Natural Philosophy in the Royal Institution* . 



AS a mechanical model of the electric machinery at work 

 in the induction of currents Maxwell employed differ- 

 ential gearing ; and an apparatus on this principle, designed 

 by him, is in use at the Cavendish Laboratory. Wishing to 

 show something similar in a recent course of lectures, and not 

 having differential gearing at my disposal, I designed more 

 than one combination of pulleys, the action of which should 

 be analogous to that of electric currents. These eventually 

 resolved themselves into Huygens's gearing, invented, I 

 believe, in connexion with the winding of clocks. As this 

 apparatus is easier to understand than differential gearing, 

 and the parts of which it is composed are more likely to be 

 useful for general purposes in a laboratory, I have thought 

 that it might be worth while to give a description, accom- 

 panied by an explanation of the mode of action. 



Two similar pulleys, A, B, turn upon a piece of round steel 

 fixed horizontally f . Over these is hung an endless cord, and 



* Communicated by the Physical Society : read May 16, 1890. 

 t Light wooden laths, variously coloured and revolving with the 

 pulleys, render the movements evident at a distance. 



