g$2t> ZV. Darwin’s Experiments on the 
chil-linefs on coming Into an atmofphere of temperate warmth, 
after having been fome time confined in a very warm room: 
and hence the ftomach, and other organs of digeftion, of 
.-thofe who have been habituated to the greater ftimulus of fpi- 
rituous liquor, are not excited into their due adtion by the lefs 
ftimulus of common food alone ; of which the immediate con- 
iequence is indigeftion and hypochondriacifm. 
III. OF SPECTRA FROM EXCESS OF SENSIBILITY. 
? ; ' , ■ ; ■ ) 
The retina ■ is more eafily excited into ablion by greater irritation 
after having been lately fubjeSed to lefs . 
1. If the eyes are clofed, and covered perfectly with a hat, 
for a minute or two, in a bright day ; on removing the hat a 
red or crimfon light is feen through the eye-lids. In this ex- 
periment the retina, after being fome time kept in the dark, 
becomes fo fenfible to a fmall quantity of light, as to perceive 
diftindlly the greater quantity of red rays than, of others which 
pafs through the eye-lids. A fimilar coloured light is feen to 
pafs through the edges of the fingers, when the open hand is 
oppofed to the flame of a candle. 
2. If you look for fome minutes fteadily on a window in 
the beginning of the evening twilight, or in a dark day, and 
then move your eyes a little, fo that thofe parts of the retina, 
on which the dark frame-work of the window was delineated, 
may now fall on the glafs part of it, many luminous lines, 
reprefenting the frame- work, will appear to lie acrois the glafs 
panes: for thofe parts of the retina, which were before leaft 
ftimulated by the dark frame-work, are now more fenfible to 
light 
