46 ESSAYS anp OBSERVATIONS 
monftrate, that the idea of green is a con- 
fufion or mixture of the ideas of yellow 
and blue; the idea of white, a mixture 
of the ideas of all the colours; and, in 
general, the ideas of all compound co- 
lours, a mixture of the ideas of their con- 
{tituents? In the experiments which Sir _ 
Ifaac Newton performed with the toothed 
inftrument, the component colours are 
not, indeed, prefented to the eye all at 
once; yet they follow one another in fo 
rapid a fucceffion, that their refpective 
impreflions remain in the eye till they are 
renewed, and therefore they muit arfect 
the mind all at once*. Ifa piece of pa- 
per 
* It is in this manner that philofophers explain (Ne: 
Opt. Quer. 16.) the appearance of a fiery circle, which 
is made by a burning body whirled about fwiftly. We 
{hall here give an account of fome other phenomena that 
flow trom the fame principle, 
If a white rod be moved rapidly backwards and for- 
wards with an angular motion, the whole circular {pace 
which it runs over will appear whitifh ; but not equally 
fo, being tainteft and moft dilute in the middle, and 
brighter towards the two fides, which feem to be di. 
flinctly terminated with two white rods interfeéting each 
other in the center of rotation, (See Tap, ili. Fig, 7.) 
i The 
