( ^ 4 ^ ) 
ferve in Sir Ifaac Newton*^ oblong SpeBrum, - Un' 
der this was a fpace, of a Breadth confiderably lefs than 
that of the Limbus of the Rainbow, in which I could 
not diftinguiih any Colours : Still lower was a faint in- 
V terrupted Arch of red, inclining to purple, which ap- 
pear’d and yanilh’d feveral times, while I was intent 
upon obferving it. ^ - 
My Sufpicion about this Pha^nomenon is, that the 
extraordinary Rednefs in the purple of the firft Rain- 
bow, is owing to the Mixture of the red Rays of a^ fe- 
cond Series of Colours, with the purple Rays of the 
firft j that the colourlefs Space confifted of Rays which 
are too weak to affedthe Sight with diflincl Colours y 
and that the innermoft broken Arch was the ending 
of afecond and beginning of a third Iris. 
» • ■ 
L*. S. I forgot to tell you, that as in the Account I 
fend you here, I faw the purple of the fecond Iris 
without the other Colours, To I have feen the other Co- 
lours, but not very diftind, without the purple ; as al- 
fo, that I could never fee more than one Series of Co- 
lours near the Horizon. 
t • . 
\ . I 
*Fetworth, March ix. ‘ . 
Y Eflerday in the Evening, about a quarter before 
Six, Wind S. W. we had one of the fineft Rain- 
that ever I beheld. 
The ‘firft Series of Colours was as ufual, only the 
Purple had a far greater Mixture of red in it, than I 
have ever feen in the prifmatick Purple: Under this 
was a colour’d Arch, in which the green was fo pre- 
dominant, 
I 
