2S M&bMpasmoN or Iight. 



lino) in diameter, by means of which we could allow si 



small coloured pencil to fall on the cloth, while all the rest 



was dark. We conld easily ascertain, that this little pencil, 



taken successively from the different colours, was simplified 



as much as possible by refraction ; for the circular spot, 



examined some distance with a prism, was not at all irregular. 



We then passed through tlie small hole a pencil of' very 



decided blue ; and in this respect our latitude of choice was 



great, since in our spectrum the blue had an extent of more 



Blue light than 54 millimetres. (2 inches) Th^ blue spot being well 



transmitted f ormef j on the cloth, the green phial was placed before the 



through a green ' w * r 



medium was hole; when the light of the spot was immediately much 



preen; weakened, and its colour chanced to green. On substituting 



through violet, ' b H - , » 



was violet. the violet phial in the place of the green, the spot became 



violet. This experimeut was repeated several times, that 



we might convince ourselves of the fact, and succeeded 



uniformly. 



Y allow changed ^ ne *" a * w ' f ^ tne y*dl°"' succeeded in like manner; it 



to red and was changed successively to red and green, according to the 



green " substance opposed to the rays. 



Experiment Another day these experiments were repeated wkh some 



varied by little alterations. When the small round image fell upon 



image from * ne doth, we went behind to look at it; and found that it 

 behind the passed through, appearing on the back of the cloth, which, 

 a coloured sub- was muslin we ^ stiffened with starch. In this nay we could 

 stance put make our experiments more conveniently, as we had only tc* 

 e ore ic eye. C0TCr 0lir e y e w j^ a co i afcsrCf j substance, and look at the 

 Blue light, as little spot through it. When the spot was formed by blue 

 before. Ii j^ht> it appeared green, or violet, according to the sub- 



Stance interposed. Through a red substance no light was, 

 seen: a proof, that the preceding effect did not arise from 

 white light mixed with blue. If it were viewed through an 

 orange glass, the property of which is to absorb only the 

 blue and violet rays, the spot appeared green; a proof 

 that it was formed in reality bv green and violet rays. 

 Yilow the Finally the yellow spot exhibited similar appearances; 



same ' altogether invisible through a violet substance, it shewed 



itself green or red through substances of these colours. 

 Argument 1 ? for Such are the results, that confirm my opinion of the 

 coioursfTJd VC tfewentary parts of light. Now let these be combined with 

 green, And the 



