'26 Prof. Forbes's Researches on the Vibrations which take place 



metals highest on the scale: An example will illustrate the 

 mode of operation. 



32. 30th July 1831. — Experiments made with masses of 

 silver, copper and gold, placed in a vice, and heated with a 

 spirit-lamp until a globule of water evaporated in violent ebul- 

 lition from its surface. The cold metals were employed as 

 bars. 



Hot Silver. 



Cold Lead. Vibrates perfectly well. 



Tin. Apparently as well as Lead. 



Zinc. Vibrates very well. 



Iron. Vibrates distinctly; but apparently less 



than Zinc. 



Brass. Not decisively. 



Copper. Not at all. 



Hot Copper. 



Cold Lead. Vibrates very well. 



Tin. The same. 



Zinc. Not at all ; even where the temperature 



of the Copper is raised much above 212°. 



Iron. Vibrates very imperfectly. It appears, 



however, more active than Zinc. I have 

 formerly observed a decisive vibration of Hot 

 Copper upon Cold Iron (11th July). 



Brass. No Vibration. 



Hot Gold. 



Cold Lead. Vibrates quite readily. Nearly as with 

 Copper. 



Tin. Nearly as with Copper. 



Zinc. Ditto. 



Iron. No distinct vibration, but with consi- 

 derable heat of the lamp approaches to it ; it 

 is rather more disposed to vibrate than Zinc. 



By experiments analogous to these, we may see how the 

 position of any metal is fixed by a variety of tests, which af- 

 ford mutual confirmation. 



33. In the course of forming the classification of metals, I 

 was naturally led to compare it with Mr. Faraday's hypothesis, 

 that the vibration between two metals depended on the dif- 

 ference of their conducting powers for heat directly, and of 

 their expansion inversely. Finding considerable deviations 

 from this law, I was led to look for some simpler analogy. 



34. The first arrangement which presented a striking simi- 

 larity was that of the conducting powers of the metals for 

 electricity. The further examination to which this remark 



