330 Dr. W. Knight on the Vibration of healed Metals. 



sending you a shorter account than I could wish of the new 

 trials made on the vibrations of metallic bodies in the end of 

 March and beginning of April last. 



" Having frequently failed as well as succeeded with the 

 iron pokers and masses of lead, &c, and not being always able to 

 account for the failures, a simple plan of producing vibrations 

 occurred to me, which in no instance yet tails upon the greater 

 number of metals employed. This consists in placing a quan- 

 tity of a melted metal (as tin, lead, fusible metal, bismuth, 

 &c.) in a hemispherical, or, better, in a parabolic conoidal cup 

 of copper, or iron, or brass, lying above a piece of lead or 

 other metal. The oscillations of the cup thus resting upon a 

 small surface continue long after it has become solid, indeed 

 until the cup and its contents have fallen to a temperature not 

 much above that of the metal upon which they rest. I have 

 employed in many trials cups of iron, brass and copper, of 

 various sizes, from 2 to 6 inches in diameter at the top ; and 

 of melted metals, from an ounce to some pounds, of bismuth, 

 tin, lead, zinc, &c. (In case of pouring the melted metal too 

 rapidly from the ladle into the cups, and thus overturning the 

 latter, it may be steadied by a small pair of forceps for a few 

 seconds.) No vibrations could be produced above any other 

 bodies than metals: they are most striking above lead, tin, zinc, 

 antimony; more feeble above silver, gold, platina, brass, cop- 

 per. Above wrought and cast-iron, 1 could not observe them. 

 They are very distinct above slabs of the metal of reflecting 

 telescopes, and above fusible metal. The smoothness of the 

 ingots above which the vibrations are performed lessens the 

 effect greatly, or prevents it. 



" Among the most interesting trials are : 



kt 1st, 3 or 4< ounces of lead, melted and poured into the 

 parabolic cup of copper, resting above the ingot of 1 pound of 

 tin with uneven surface. The tremors loud, quick and large; 

 a peculiar crackling noise is heard, which I cannot distinguish 

 in character from the noise of the same kind which ensues 

 on bending a piece of block tin held close to the ear. On 

 compressing the tin ingot with the fingers, the sound does not 

 cease, but assumes a sort of stifled character: on removing the 

 fingers, the former crackling noise is resumed. The fingers 

 feel distinctly the vibration communicated to the ingot by the 

 heated cup. 



" 2nd, The same placed on an ingot of 1 pound of zinc. 

 The vibrations commenced immediately on pouring out the 

 lead : they were small, rapid and equal, (not of an unequal 

 sort like those above antimony): the sounds louder than above 

 any other metal. They cease on pressing the ingot between 

 the fingers ; when resumed, there seemed some difference of 

 tone : the stopping at the end sudden and distinct. 



