220 [Dec. 12, 



duce upon the eye at any moment the impression of double the num- 

 ber of elevations that actually exist at that moment. Elevations that 

 appeared to be about -J- th of an inch asunder emitted the note F. 



7. The position of the elevations in very narrow rings of mercury 

 is generally uniform, i. e. in lines radiating toward the centre of the 

 vessel when the mercury is undisturbed ; but with rings Jth of an 

 inch wide or upwards the elevations of different portions of the ring 

 frequently fluctuate in their positions ; and under much rarer condi- 

 tions the whole ring of elevations revolves (and sometimes rather 

 quickly) round an imaginary axis in the centre of the vessel, some- 

 times in one direction and sometimes in the other ; but what the 

 conditions are that determine the rotation or its direction I have not 

 investigated further than to ascertain that the vibrations are not in- 

 fluenced by a strong magnet. The surface of the negative or 

 vibrating mercury never exhibited nodal points. 



8. In addition to the elevations which emit sounds, there are other 

 movements of greater amplitude, . e. undulations about Jth of an 

 inch in length ; and also other motions of a more violent kind in 

 negative pools of mercury, consisting of upheavals of mercury in large 

 masses at irregular distances from each other, as if large bubbles of 

 gas were beneath (but no gas was observed), especially in a solution 

 composed of 2 ounces of hydrocyanic acid and 100 grains of hydrate 

 of potash, on first electrolysing it. Both these motions, like the 

 previous ones, occur at the cathode, but neither of them are attended 

 by appreciable sounds. On rare occasions, with the full power of the 

 battery exerted upon the solution given (3), undulations have also 

 been observed in the positive mercury surface, but they emitted no 

 perceptible sounds. 



9. I have not given a full description of all the numerous appear- 

 ances of the various movements, as similar phenomena (though pro- 

 duced by other causes) have been minutely described by Mr. Faraday 

 in the Philosophical Transactions of the Royal Society, 1831 ; and my 

 remarks will be almost entirely confined to the vibrations that produce 

 sounds, because the other electrolytic movements have already been 

 to a great extent observed and examined by previous investigators. 



10. The phenomenon of definite sound is limited to those crispa- 

 tions whose widths lie within certain limits ; when the widths between 

 the elevations enlarge beyond ^th of an inch, the sounds cease. Fre- 



