( S-3 ) 
AnExtr^oi of another helter of ^rf.Newrorij written totheVu'- 
hlifber the loth of January 167-6, reUtir/g to the fame Avgu^ 
menu 
Y Mr. G^/^r<?/Vs Letter* one might MpeS, that Mr- 
Linus tryed the Experimenr fome ocher way than I 
did; and therefore I fliallexpeft, till his friends 
havetryeditaceordingtomy late Direflions. In 
whichtryalkmaypoffibly be a further guidance tv™Lm"the Pu- 
re them,to acquaint them, that the Prifm cafts hViihtr, vecemb.\%; 
from it feverai Images : One is.that OUonz one of ^^p- ll^^ i-''^' » 
Colours which i mean ; and this is made by two having been aScho- 
Refraftionsonly. Another there is, made by two l2rofMr,z/;7«5,now 
Refraftions and an intervening Reflexion; and JnT^'e^onfa^^^^^^ 
this is Round and Colour kfsy if the Ang^esof the thefe words , to 
Pdfm beexacStly equal ; but if the Angles at the ""'^''f Nir.NerPto», 
« n A. » /- I i • -n 1 I 7 r to whom It was com- 
Refledling bafe be not equal , it will be colour rrunicated , feems 
and that fo much the more, by how much unequal* ^f^^J^^^p refpeaj 
ler the Angles are, but yet not much un- ^lYEx'pef'imZ'a^^^^ 
lefs the angles be very unequal. A third -JvAZgG a"c/a^ain , and cai^ 
there is, made by one fingle Reflexion, and this is trit !\lrV'Ier 
always and colourlefs. The only d anger is made difficnifyto /kew 
in miftaking the fecond for the firfl. But they are ^ll^'^^^'f^'^^^^^^^'' 
diftinguifl]able not only by the Length and Lively \Xk Ihlmbir l^Tt 
colors of the Jirfl, but by itV different Motion r^a^doh^it.or fhevP' 
too : For, wbilft the Prifm is turned continually ff,^ 'fXl 
the fame way about ii*s4jffer, the fecond zx\d^third ferpoint of Expert'- 
movefwifdy, and go always on the fame way till '"^'^ ivj/". Newton 
1/- \ r n rt i cannot be more confi- 
theydifappear ; but the firjt movGS flow, znd \i,„ton hk/ide, than 
grows continually flower till it be ftationary, and ^« arehere on the 
then turns back again, and goes back fafter and fa- 
fter, till it vanifliin the plae^ where it began to the di'verftty of pia- 
5»r>n^:ir chg ihe Frifm, or the 
^PP^^*^* blgntf.cftheHoh.or 
fome other fuch ciy 
cumflance , he the caufe cf the differ en^t he tx^j;^ them ^ Newton Expert mtjA 
ypf II hardly fland» 
If without darkning their Room they hold the Prifm at thm^ 
window in the Sun's open Light, in fuch a poflure that it's axi^ bs 
