Mr. T. Wedgwood’s Experiments and Observations , &c. 271 
from the crucible, still looking within it, I was surprised to 
see the appearance reversed, the polished cylinder continuing 
to shine for some time after the blackened one had ceased. 
Cylinders of gold, and of iron, treated in the same manner, 
gave the same general result ,* but the differences between the 
polished and the blackened ones were not so remarkable in 
these, as in the silver. 
I repeated this experiment many times, and found, by ob- 
servations with a stop-watch, that the blackened silver cylinder 
began to shine, at a medium, in two-thirds of the time which 
the polished one required ; and that, after its removal from 
the crucible, it continued to shine only two-thirds of the time 
that the other did. For this latter observation, I was obliged 
to make a little variation in the apparatus ; the tube itself be- 
coming frequently so hot, as to make the cylinders continue 
longer red than they otherwise would have done : I therefore 
took them out of the tube, to suspend them by a fine wire, 
and then heating them in the ignited crucible as equally as 
possible (for they cannot be made to exhibit to the eye the 
same precise tinge of redness), I removed them immediately 
into a dark place. 
From this experiment it would seem, that a great part of the 
light emitted by the cylinders was absorbed from the red hot 
crucible, as the blackened one, which absorbs most rays, not 
only became first red, but likewise shone brightest. The fol- 
lowing experiment, however, affords a different conclusion. 
EXPERIMENT II. 
An earthen ware pipe, of a zig-zag form (Fig. 2.), was placed 
in a crucible, which was filled up with sand, the two open 
N n 2 
