620 OCULAR SPECTRA. S E cf . AL. 6. 



after it has been fatigued by one kind of action, it 

 fpontaneouily falls into the oppofite kind. 



i. Place a piece of coloured filk, about an inch 

 in diameter, on a fheet of white paper, about half 

 a yard from your eyes ; look fteadily upon it for a 

 minute ; then remove your eyes upon another part 

 of the white paper, and a fpedtrum will be feen of 

 the form of the filk thus infpe&cd, but of a colour 

 oppofite to it. A fpectruui nearly fimilar will ap- 

 pear if the eyes are clohd, and the eyelids fhaded 

 by approaching the hand near them, fo as to permit 

 fome, but to prevent too much light falling on 

 them. 



Red filk produced a green fpe&rum. 



Green produced a red one. 



Orange produced blue. 



Blue produced orange. 



Yellow produced violet. 



Violet produced yellow. 



That in thefe experiments the colours of the fpec- 

 tra are the reverfe of the colours which occafioned 

 them, may be feen by examining the third figure in 

 Sir Ifaac Newton's Optics, L. II. p. i, where ihofe 

 thin laminae of air, which reflected yellow, tranf-' 

 mined violet ; thofe which reflected red, tranfmitted 

 a blue green ; and foof the reft, agreeing with the 

 experiments above related. 



2. Thefe reverfe fpe&ra are fimilar to a colour, 

 formed by a combination of all the primary colours 

 except that with which the eye has been fatigued in 

 making the experiment : thus the reverfe fpedruni 

 of red muft be fuch a green as would be produced 

 by a combination of all the other prifmatic colours. 

 To evince this fact the following fatisfactory expe- 

 riment was made. The prifmatic colours were laid 

 on a circular pafteboard wheel, about four inches in 

 diameter, in the proportions defcribed in Dr. Prieft 

 ley's Hiftory of Light and Colours, pi. iz. fig. 83 



excep 



