C ®7° 2 
XIII. Continuation of a Paper on the Production of Light 'and 
Heat from different Bodies. By Mr. Thomas Wedgwood ; 
communicated by Sir Joseph Banks, Bart. P.R.S. 
Read May 10, 1792. 
EXEPRIMENT I. 
In order to discover what effect the light of the burning fuel 
has upon incombustible bodies, I fixed into the end of a tube 
of earthen ware * two equal cylinders of silver, with polished 
surfaces, half an inch in length, and a quarter of an inch in 
diameter (see Tab. V. Fig. 1.) ; one of the cylinders was painted 
over, except the end within the tube, with a thin coat of incom- 
bustible black colour, to make it absorb the incident light ; the 
other, intended to reflect , was left with its polished surface. 
Applying my eye to the opposite extremity of the tube (which 
it fitted exactly, so that no extraneous light could enter), and 
directing it towards the two polished ends of the cylinders, I 
held the tube within a red hot crucible, surrounded by burn- 
ing coaks, and continually turned it round, that both cylinders 
might be equally exposed to the light, and heat. The result 
was, that the end of the blackened cylinder began to shine a 
considerable time before that of the polished one, and re- 
mained constantly somewhat brighter : on removing the tube 
• When earthen ware is mentioned in this paper, the cream-coloured or queen’s 
ware is meant. 
