( 411 ) 
II. An Account of fome Experiments of Light and 
Colours , formerly made hy Sir Ifaac Newton, and 
mention d in his Opticks , lately repeated before the 
Royal Society by. J. T. Defaguliers, F. R. S. 
t 3 JIT1303 £}j ffl ' . 
T HE manner of feparating the primitive . Colours of 
Light to fuch a Degree, that if any one of the fepara* 
ted Lights he taken apart , its Colour (hall he found unchange- 
able,; re as not puhlifhed before Sir if Newton * Opticks carpe 
abroad. For want of knowing how this was to be done, 
fome Gentlemen of the Englijh College at Liege, and Mon- 
jieur Mariotte in France, and fome others took thofe for pri- 
mitive Colours, which are made by immitting a Beam of the 
Sun's Light into a dark Room through a fmall round Hole, and 
refracting the Beam by a triangular Prifm of Glafs placed at 
the Hole . And by trying the Experiment in this manner, 
they found that the Colours thus made were capable of change, 
and thereupon reported that the Experiment did not fucceed. 
And lately the Editor of the Ada Eruditorum for Odober 
1 713. pag- 447, dejired that Sir If. Newton would remove 
this Difficulty. Objediones, inquit, quasViridodi turn in 
Gallia turn in Anglia contra illam [de Coloribus] Theori- 
am fecere, feliciffime diluit Vir perfpicaciflimus Newt onus, 
quemadmodum exTranfadidnibus Anglicanis N. 84. 85-, 
88, 96, 973111, 118 abupde coriftat. Undemul- 
ti optant utmentem fuam aperire dignetur,de difficultate 
ab ingenioiifTimo Mariotto, rerum naturalium (dum vive- 
ret) fcrutatore indefefio nee infelici, in Tradatu de Co- 
loribus p. 107. & feq. contra earn mota. In diftantia fci- 
licet 15 circiter aut 30 pedum, charta excemt radium foli- 
dumper exiguum foramen in cameram obfcuram iiamiffam, 
Yyy & 
