Vibration of Heated Metals. 139 



17. A short bar of heated copper was placed on an iron block 

 rounded on the surface, and being nicely balanced on the centre 

 of the rounded part, showed the vertical motion. 



18. When the blocks have acquired nearly the same tempe- 

 rature as the bars, the sound and motion cease. 



19. I could not perceive the slightest vibration when the 

 heated bar was placed on a small block of platina. 



20. Vibration is prevented by rubbing the surface of the lead 

 block with mercury, oil, plaster of Paris, or by oil-gilding ; and 

 also if a piece of thin writing paper be interposed between the 

 bar and the block. 



21. Air blown with a pair of bellows on the heated bar when 

 vibrating, does not affect the tremors. 



22. By means of a frigorific mixture, I cooled the lead block 

 to 8 F., and placed on it a brass bar at the temperature of the 

 air in the room, but no vibration took place. 



23. I have not observed any vibration of the heated bars when 

 laid on solid blocks, either rough or smooth, of copper, zinc, anti- 

 mony, brass, marble, plaster of Paris, or clay, or on lead with a 

 piece of sheet-brass soldered on it, although I have tried bars and 

 blocks of different sizes and shapes. 



24. Bars made of pewter, tin, or lead, heated and placed on 

 the cool blocks of either the soft or hard metals above named, do 

 not vibrate. 



45. A cool bar of lead, placed on a heated block of brass or 

 copper, vibrates. 



26. A block of lead, laid on the flat upper bar of a heated 

 grate, shows the vibrations, accompanied with sound. 



27- The heated bar was placed upon a block of copper, in 

 which a number of holes, |th of an inch in diameter, and |th of 

 an inch deep, were drilled, but no vibration took place. 



28. If the heated bar be ground smooth on the resting part, 

 and the block of lead be also very smooth, no vibration takes place. 



