138 Mr TREVELYAN'S Experiments on the 



consequently the tone produced by it, is altered, and sometimes 

 ceases altogether. 



6. A common poker, heated and placed on a lead block, vi- 

 brates, producing deep tones also in the key of E major. 



7. By balancing the bar in a horizontal position on a narrow 

 lead block, rounded on the part upon which the bar rests, the vi- 

 bration is displayed much more distinctly ; the handle of the bar 

 moves vertically, and the part resting on the block laterally also. 



8. A rod 10 or more inches long, flattened in the centre to 

 prevent it slipping, with a ball at each end, when placed across a 

 heated vibrating bar, and increasing the motion, renders, by the 

 length of its arms, the lateral movements much more conspicuous. 



9. The longer the rod is, the slower are the movements of 

 the heated bar, but its oscillations are so much the greater. 



10. A thick ring of copper, 5 inches in diameter, when heat- 

 ed and hung on a lead bar, vibrates backwards and forwards ; and 

 when laid on a narrow block of lead, upwards and downwards. 



11. The heated bars vibrated on a piece of thin sheet-lead, 

 either placed loosely or soldered on a block of hard metal, and on 

 a lead block burnished with gold-leaf. 



12. The vibration continues in the exhausted receiver of an 

 air-pump. 



13. The brass bar, after being heated in boiling water vibra- 

 ted when placed on the lead. 



14. A copper bar vibrated when heated and placed on cylin- 

 ders of brass, or of an alloy of copper with an edge tVth of an 

 inch in thickness ; also on the bottom of a copper box about 1 

 inch in diameter, and slightly cupped out, leaving a ridge all 

 round, on which the bar rested. 



15. The same effect was produced on the bottom of a glass 

 tumbler, but these effects are frequently difficult to be obtained. 



16. The bars vibrate best when placed on blocks of lead with 

 the surfaces somewhat rough. Both metals should be also kept 

 clean, and free from oxidation, which impairs the vibration. 



