In	the	Sun’s	Beam	which	was	propagated	into	the	Room	through	the	hole	in	the	Window-shut,	at	the	distance	of	some	Feet	from	the	hole	,	I	held	the	Prism	in	such	a	Posture	,	that	its	Axis	might	be	perpendicular	to	that	Beam.	
Then	I	looked	through	the	Prism	upon	the	hole,	and	turning	the	Prism	to	and	fro	about	its	Axis,	to	make	the	Image	of	the	Hole	ascend	and	descend,	when	between	its	two	contrary	Motions	it	seemed	Stationary,	I	stopp’d	the	Prism,	that	the	Refractions	of	both	sides	of	the	refracting	Angle	might	be	equal	to	each	other,	as	in	the	former	Experiment.
In	this	situation	of	the	Prism	viewing	through	it	the	said	Hole,	I	observed	the	length	of	its	refracted	Image	to	be	many	times	greater	than	its	breadth,	and	that	the	most	refracted	part	thereof	appeared	violet,	the	least	refracted	red,	the	middle	parts	blue	,	green	and	yellow	in	order.	
The	same	thing	happen’d	when	I	removed	the	Prism	out	of	the	Sun’s	Light,	and	looked	through	it	upon	the	hole	shining	by	the	Light	of	the	Clouds	beyond	it	.	
And	yet	if	the	Refraction	were	done	regularly	according	to	one	certain	Proportion	of	the	Sines	of	Incidence	and	Refraction	as	is	vulgarly	supposed,	the	refracted	Image	ought	to	have	appeared	round.	
So	then	,	by	these	two	Experiments	it	appears,	that	in	Equal	Incidences	there	is	a	considerable	inequality	of	Refractions	.	
But	whence	this	inequality	arises,	whether	it	be	that	some	of	the	incident	Rays	are	refracted	more,	and	others	less,	constantly,	or	by	chance,	or	that	one	and	the	same	Ray	is	by	Reflection	disturbed	,	shatter’d,	dilated	,	and	as	it	were	split	and	spread	into	many	diverging	Rays,	as	Grimaldo	supposes	,	does	not	yet	appear	by	these	Experiments,	but	will	appear	by	those	that	follow.