ocular Speftra of Light and Colours. 323 
before expofed to the darknefs of the night, and therefore ten- 
fold more fenfible to light than the part on which the ftar or 
candle had been for fome time delineated. This pains the eye 
in a fimilar manner as when we come fuddenly from a dark 
room into bright daylight, and gives the appearance of bright 
fcintillations. Hence the ftars twinkle mofl: when the night is 
darkeft, and do not twinkle through telefcopes, as obferved by 
Musschenbroeck ; and it will afterwards be feen why this 
twinkling is fometimes of different colours when the object is 
very bright, as Mr. Mel v ill obferved in looking at Sirius. 
For the opinions of others on this fubje&, fee Dr. Priestley’s 
valuable Hiftory of Light and Colours, p. 494. 
Many fafts obfervable in the animal fyftem are fimilar to 
thefe ; as the hot glow occafioned by the ufual warmth of the 
air, or our cloaths, on coming out of a cold bath ; the pain of 
the fingers on approaching the fire after having handled fnow ; 
and the inflamed heels from walking in fnaw. Hence thofe 
who have been expofed to much cold have died on being 
brought to a fire, or their limbs have become fo much in- 
flamed as to mortify. Hence much food or wine given fud- 
denly to thofe who have alrnoft perifhed by hunger has de- 
ftroyed them ; for all the organs of the famifhed body are now 
become fb much more irritable to the ftimulus of food and 
wine, which they have long been deprived of, that inflamma- 
tion is excited, which terminates in gangrene or fever. 
