: (^092 ) 
j; Whether thetiaequal Refra'diionfj made without refpe^ 
to any iaequality of iacidenee^ be caufed by the different Re- 
frangibility of feveral Rays i or by the fplitting,. breaking or 
diffipating the iarne Ray into^diverging parts ? ^ 
2o Whether there be more than two fopts of Colours ? 
Whether Whitenefs b@ a mixture of all Colours f 
: The F^Vy? of thefe ^^ceres you 
LS^i:^^^"^^*^ ^^^^ may find already deSmio/by 
an Experiment in my former Let- 
ter r the defiga of which was to fhew. That ihe length of the 
colour 'd Image proceeded not from 'any urievennefs in the 
Glafs, or any other contm^ent Irfegularity io the Refradions. 
Amongft other Irregularities- 1 know not, what is morecbvi.- 
Gus to fafped:, than a forttiitbus dilating and fpreading of 
Light after fome fuch manner, as Des-Cartes hath defcribedin 
his iEthcreal Refractions far explicating the T^j/i? of a Come^ 
or as thQ Animadver for BOW fuppofes to be effeded by the 
5'plitting and Rafifying of his Ethereal Ipulfes* And tope 
veot the fufpicion of any fuch IrregularitieSj I told you, that 
f refr axSted the Light contrary ways with two Prifmes fuccef- 
fivelyj to deftroy thereby the Regular cffcAs of the firjl Prifrae 
by the [econd^ and to difcover the Irregular effefts by augmeut- 
ing them with iterated refra<J3:ions. Nov#, amongft other lr« 
regularities, if the firjl Prifme had fpread and dsffipated every 
ray into an indefinit number of diverging parts, the fecond 
fliould in like manner have fpread and diiOipated every one of 
thofe parts into afurther indefinite number, whereby the I. 
mage would have beenftill more dilated, contrary to the e- 
vent* And this ought to have hapned^ becaufe thofe Linear 
divergiilg parts depend ^ot qft bne ano the manner of 
tiieir Refraction*, but are every oneof them as truly and coin- 
pleatly Rays as \ whole was before its lacidenceias may ap- 
pear by ititercepting them feverallyv^ 
The reafonablenefs of this proceeding will perhaps better 
appear by acquainting you with this further circumftance* I 
fometimes placed the fecmd Priftbe M a^pofition Tranfvcrfe to 
thejfr/?^ on defign to tryjif it would make the long Image be- 
come four-fquare by refradions croffing thole that had drawn 
die round Image into a lorigoti^ Pciryifamongfl otherr Ir- 
regularities the Refra^ioH of £he#/? Prifme^ did by Sp'ittiog 
^ dilate 
