58 Inquiry concerning the Nature of Heat, 



formed respecting the nature of those rays and the 

 mode of their action. 



I had hitherto made use of but one metal (brass) in 

 my experiments ; and that was not a simple, but a com- 

 pound metal. The first subject of inquiry which pre- 

 sented itself, in the prosecution of these researches, was 

 to find out whether or not similar experiments made 

 with other metals would give similar results. 



Experiment No. 14. Procuring from a gold-beater a 

 quantity of leaf gold and leaf silver about three times 

 as thick as that which is commonly used by gilders, I 

 covered the surfaces of the two large cylindrical vessels, 

 No. i and No. 2, with a single coating of oil varnish; 

 and, when it was sufficiently dry for my purpose, I gilt 

 the instrument No. i with the gold leaf, and covered the 

 other, No. 2, with silver leaf. When the varnish was per- 

 fectly dry and hard, I wiped the instruments with cotton, 

 to remove the superfluous particles of the gold and sil- 

 ver, and then repeated the experiment, so often mentioned, 

 of filling the instruments with boiling-hot water, and 

 exposing them to cool in the air of a large quiet room. 



The time of cooling through the given interval of 

 10 degrees was just the same as it was before, when the 

 natural surface of these brass vessels was exposed naked 

 to the air. 1 repeated the experiment several times, 

 but could not find that the difference in the metals 

 made any difference in the times of cooling. 



Experiment No. 1 5. Not satisfied to rest the deter- 

 mination of so important a point on a trial with three 

 metals only, brass, gold, and silver, I now provided 

 myself with two new instruments, the one made of 

 lead, and the other covered with tinned sheet-iron, im- 

 properly, in England, called tin. 



