Prof. Forbes on certain Vibrations produced by Electricity. 359 



vibrations continued when the whole was immersed partly or 

 wholly in water, and even when flooded by a powerful continued 

 stream of cold water from a ^-inch pipe under considerable 

 pressure. Fi'om this experiment I conclude that the effect of 

 the heat developed by the electrical current in the thin upright 

 plates may be fairly considered to be reduced so low as to be 

 incapable of producing a sensible result (if such were ever the 

 case). Indeed, allowing for the resistance and friction of the 

 water tending to diminish the vibration, there is no ground for 

 thinking that the action was less energetic in the one case than 

 in the other. It is consequently reasonable to conclude that the 

 effect in question is due to the repulsive action of the electricity 

 in passing from one conducting body to another, and not to its 

 effect in producing expansion. 



Now this is precisely the effect which I attributed to heat in 

 the paper of 1833 already referred to. I therefore consider it a 

 strong confirmation of the opinion I then expressed, from which 

 I have never swerved, although it has not in general been received 

 with much favour. The importance which I attach to this new 

 confirmation, and the suggestiveness of Mr. Gore's experiment 

 on the rolling-ball, vrill be judged of from the fact, that in 1833, 

 or earlier, I had an apparatus made consisting of a bar resem- 

 bhng Mr. Trevelyan's, but longitudinally divided by a non-con- 

 ducting partition ; while the two conducting sides were furnished 

 with mercury cups for connecting them with the poles of a bat- 

 tery, the circuit being completed through the metallic base. 

 The instrument exists, or existed a few years ago, though I am 

 at present unable to find it. As well as I recollect, it was tried 

 with an old-fashioned Cruickshank's battery of fifty pairs, with- 

 out success. Indeed I now find that, even with modern appli- 

 ances, the experiment does not succeed when the circuit is only 

 closed whilst both points of bearing of the rocker touch the mass 

 or support. 



December 20, 1858. 



Since the date of the preceding notice (which was prepared 

 for being laid on the table of the Royal Society at their meeting 

 on the 20th ult.), I have continued and extended these experi- 

 ments. As they are still in progress, I will content myself with 

 mentioning two results as worthy of notice. I have obtained 

 very active vibrations of carbon (such as is used in one of the 

 elements of Bunsen's battery) resting upon brass, and also when 

 it rests upon two pieces of carbon connected with the terminals 

 of a battery. For this purpose, a battery having a certain 

 amount of intensity is requisite, in order to overcome the resist- 

 ance of carbon as a conductor ; but the vibrations arc most ener- 



