On the Vision of Colours. 45 
8. Suppose a body to reflect red rays as the num- 
ber 8, orange rays as the number 6, and blue as 5; 
and another body red 8, orange 6, and blue 6: then 
it is evident that a common eye, attending principal- 
ly to the red, would see little difference in those co- 
lours; but we, who form our ideas of the colours 
from the orange and blue, should perceive the latter 
to be bluer than the former. . 
g- From the whole of this paper it is evident, 
that our eyes admit blue rays in greater proportion 
than those of other people; therefore when any kind 
of light is less abundant in blue, as is the case with 
candle-light compared to day-light, our eyes serve 
in some degree to temper that light, so as to reduce 
it nearly to the common standard. This seems to 
be the reason why colours appear to us by candle- 
light, almost as they do to others by day-light. 
I shall conclude this paper by observing, that it 
appears to me extremely probable, that the sun’s 
light and candle-light, or that which we commonly 
obtain from combustion, are originally constituted 
alike; and that the earth’s atmosphere is properly: 
a blue fluid, and modifies the sun’s light so as to 
occasion the commonly perceived difference. 
