and the Mode of its Communication. 41 



mixed up with the same size, I now washed off the 

 black paint and painted the sides of the instrument 

 white, with whiting mixed up with size ; and, on repeat- 

 ing the experiment, the results were as follows : 



Time of cooling through 

 - the given interval. 



The instrument Nq. I, naked, 55^ min. 



The instrument No. 2, painted white, . . . 36 " 



As in both the two last experiments it was found 

 necessary to paint the body of the instrument three or 

 four times over, in order to cover the polished metal so 

 completely as to prevent its shining through the paint ; 

 this, of course, occasioned the surface of the metal to be 

 covered with a thick coating of size, which, no doubt, 

 affected very sensibly the results of the experiment, and 

 rendered it impossible to determine, in a satisfactory 

 manner, what the effects really were, which were pro- 

 duced by the different colours used in the two experiments. 



Experiment No. 1 1. With a view to throw some more 

 light on this interesting subject, having washed off the 

 paint from the instrument No. 2, I now rendered its 

 sides of a perfectly deep black colour, by holding it over 

 the flame of a wax candle ; and, repeating the usual ex- 

 periment, the results were as follows : 



Time of cooling through 

 the standard interval. 



The instrument No. i, naked, ..... 55^ min. 

 The instrument No. 2, blackened, .... 36^ " 



In order to ascertain the quantity of matter which 

 composed this black covering, I weighed a small piece 

 of clean and very fine linen ; and, having wiped off 

 with it all the black matter from the body of the instru- 

 ment No. 2, in such a manner that the whole of it re- 

 mained attached to the linen, I weighed it again, and 



