2 74 Mr. T . W edg wood's Experiments and Observations 
has no particular attraction to light in a quiescent state, that is, 
when combined, as heat, with other matter. 
EXPERIMENT IV. 
Three equal cylinders of glazed earthen ware were fixed in 
the end of a tube (like the two silver ones in Fig. 1.) ; one of 
them blackened ; another gilt, all but the ends within the 
tube ; and the third with its glassy surface. These, treated in 
the same manner as the silver cylinders, in the first experiment, 
all became red at the same time. Without taking them out of 
the tube, I removed the whole from the fire, and, still keeping 
my eye upon their ends, observed them all to disappear to- 
gether. 
To account for the simultaneous ignition of these three cy- 
linders, it must be considered, that earthen ware being a very 
slow conductor of heat, the surfaces of all of them are, probably, 
heated to redness some time before any such appearance takes 
place in the ends within the tube. Now it is not unlikely, 
that the black matter, the gold, and the glaze, when red hot, 
may reflect light equally ; and, in that case, there should be no 
perceptible difference in the time of ignition of the ends within 
the tube, except the little advantage gained by the blackened 
one before its black coat becomes red hot, which is partly coun- 
terbalanced by the powdery matter (of which the coat consists) 
obstructing the transmission of heat. The surfaces of the silver 
cylinders (experiment i.) on the contrary, do not become red 
any sensible time before the ends within the tube, the metal 
conducting the heat rapidly through its whole mass. 
An earthen ware cylinder, fastened in the end of an earthen 
