C 43 ] 
thicker in fome parts than other, and the Spanifh 
white the fame : on this I fufpedted there muft be 
fome miftake in the Spanilh white and made the en- 
quiry mentioned in the note * pag. 41. 
To obviate the inequality of the ground in the 
firft experiment; 
Experiment II. 
A piece of old wainfcoat (oak board) i of an inch 
thick, which having been part of an old drawer, 
was not likely to fhrink on being brought near the 
fire ; this was fmoothed with a fifli-fkin, made quite 
warm before the fire, and then with a brufh dipped 
in white wax, melted in an earthen pipkin fmeared 
all over, and applied to the fire again, that the wax 
might be equally thick on all parts of the board, a 
ground was laid (on the waxed board) with levigated 
chalk mixed with gum water (viz. Gum Arabick 
diflolved in water) : When it was dry, I painted it with 
a kind of landfldp, and purfuing the method laid 
down by Count Caylus, brought it gradually to the 
fire ; I fixed the pi&ure on a fire fcreen which would 
preferve the heat, and communicate it to the back 
part of the board, this was placed firfl: at the dis- 
tance of three feet from the fire, and brought for- 
ward by flow degrees till it came within one foot of 
the fire, which made the wax fwell and bloat up the 
picture; but as the chalk did not abforb the wax, the 
picture fell from the board and left it quite bare. 
G 2 
Exp e- 
