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II. Optical Experiments made in the Beginning of 
Auguft 17*8) before the Treftdent and federal 
Members of the Bpyal Society , and other Gentle- 
men of federal Nations , upon Occafion of Signior 
Rizzetti’x Opticks , with an Account of the faid 
Book, By J. T. Defaguliers, L L. D. and 
F. % S . 
S Ome Time in the Year 1712, Signior Gizlanzoni , 
an Italian Gentleman, fhew’d me a Paper of Signi- 
or John Rixzetti, wherein he denied the different 
Refrangibility of the Rays of Light, becaufe an Ex- 
periment mentioned in Sir Ifaac Newton's Opticks (B.i. 
Brop. 1. Exp. 2.) concerning an oblong Paper paint- 
ed half blue and half red (whole Image projeded 
by a Lens upon a white Paper at a confiderable Di- 
ftance became diftind in its blue half, nearer the Lens 
than in its red half) had not fucceeded with him, tho* 
after many Trials. Sir Ifaac Newton being acquaint- 
ed with this, delired me to repeat his Experiment above- 
mentioned, which 1 did at my own Houfe, before him 
and Signior Gizlanzoni and fome other Perfons, who 
were fatisfied with the Succefs of it, according to 
Sir Ifaac Newton's Aifertion. Afterwards on the 13 th 
of ^December 1722, I again repeated the Experiment 
before the Royal Society , with the fame Succefs, the 
full Account of which is printed in the Thilofophical 
Tranfatlions , Number 374. After this, Signior 
Gizlanzoni read me a Letter from Signior Rizzetti , 
wherein he faid j “ He wanted to know whether the 
“ Expe- 
