On Currents of Electricity produced by Vibration. 261 



with the heated metal and causes so sudden a production of 

 steam as to burst the boiler. 



I feel, however, great difficulty in conceiving the possibility 

 of water within a steam-boiler existing in the spheroidal con- 

 dition. The coarse rough surface which the interior of the 

 boiler presents to the water is extremely unfavourable to the 

 spheroidal state; and there is every reason to believe that the 

 separation could not exist in part of the boiler without exist- 

 ing throughout the whole. But be this as it may, the exces- 

 sive heating of the boiler is the real cause of the mischief; and 

 unless it can be shown that the spheroidal state of the water is 

 the cause and not the effect of the boiler becoming red-hot, the 

 explanation appears to me to amount to nothing. 



M, Boutigny, with more reason I think, also conceives that 

 the spheroidal condition of water has an important bearing 

 upon the art of tempering steel. Whatever promotes contact 

 between the heated steel and the water into which it is plunged, 

 must accelerate the cooling and increase the hardness of the 

 steel. Now it has been shown that the higher the boiling- 

 point of the liquid, the higher is the temperature of the metal 

 necessary to preserve separation ; and hence-probably the rea- 

 son why artificers can harden steel more effectively in salt and 

 water than in water alone, because the addition of salt raises 

 the boiling-point of the water. 



The remainder of M. Boutigny's experiments do not involve 

 any other principles than those I have already touched upon, 

 and I shall not, therefore, trouble your readers by any obser- 

 vations upon them. 



Newcastle-upon-Tyne, W. G. ARMSTRONG. 



August 9, 1845. 



XXXVIII. On Currents of Electricity produced by the Vibra- 

 tion of Wires and Metallic Rods. By William Sullivan, 

 Esq."^ 

 ¥N reading over a paper of Seebeckfj in which he observed 

 •*■ that when a compound bar of bismuth and antimony was 

 heated at the junction of the two metals, a peculiar sound was 

 heard to accompany the deflection of the galvanometer-needle, 

 I thought at the time that if a similar sound could be pro- 

 duced by vibration, a current might in all probability be de- 

 veloped. Although I soon found that the sound so produced 

 had nothing whatever to do with electricity, I did not give up 

 the idea that electricity was more intimately connected with 



* Communicated by the Author. 



f Ueberdie Magnetische Polarisation der Metalle und Erzedurch Tem 

 peratur — -Differenz in PoggendorflTs Annul., vol. vi. p. 269. 



