( 435 ) 
Sheen, and the ref ratting Angle thereof he fixty Degrees or 
above. In this manner the Experiment may he tried with 
Succefs, hut the Trial will be lefs troublefome if it be made in 
fuch a manner as is defer ibed in the foutth Proportion of the 
fir ft Book of Sir If Newton’* Optzcks. 
Sir Ifaac Newton therefore, upon reading what has been cited 
out of the Ada Eruditorum, defined Mr aguliers to try the 
Experiment in the manner deferibed in the jaid Propofttion ; 
and he tried it accordingly with Succefs before feveral Gentle* 
men of the Royal Society, and afterwards before Monfieur 
Monmort and others of the Royal Academy of Sciences ; 
and ft ill (hews it to thofe who defire to fee it. How this and 
other concomitant Experiments were tried and fucceeded, is 
deferibed as follows. 
EXPERIMENT I. 
Having few’d together end* wile two Pieces of Ribbon 
four Inches long each, the one blew and the other red, 
whole common Breadth was J- of an Inch ; I caus’d it to 
be held in fuch manner, that the Light which fell from the 
Clouds thro’ the Window was lb refleded, that the An- 
gle made by the Rays of Light, which came in at the 
Middle of the Window, with the Plane of the Ribbon pro- 
duced, was equal to the Angle made by a Line drawn from 
the Ribbon to my Eye and the faid Plain of the Ribbon. 
My Eye was plac’d as far behind the Ribbon as the Win- 
dow was before it, the Dillancefrom which to me was 
about 1 2 Feet. Then looking thro’ a Prifm at the Ribbon, 
it appear’d broken alunder in the Place where the blew 
and red Half join’d. If the Prifm was held with the refra- 
ding Angle downwards (or laid with one of its Planes 
flat upon theNofe) the blew Half of the Ribbon appear’d 
to be carried down lower than the red, as at B, R in Fig. i. 
but if the reloading Angle of the Prifm was turn’d up* 
Y y y 2 wards 
