( 3078 ; 
parts of the Sun^ could not make thera after deculTation diverge 
at a fcnfibly greater angle, than that at which they before conver- 
ged ; which being, at moft, but about 31 or 32 minutes, there 
ftill remained feme other caufe to be found out, from whence it 
could be 2 degr* 49*. 
Then 1 began to fufpeft, whether the Rays^ after their tr ajeitf* 
on through the Prifme» did not move in curve lines, and accord- 
ing toiheirmore or lefs curviry tend to divers parts of the wall. 
And itincreafed aiy fulpition, when I reraembred that I had ofreo 
feen a Tennis ball, ftruck with an oblique Racket, defcribe (uch a 
curve line. For, a circular as well as a progreflive motion being 
cominunicated to it by that ftroak, its parts on that fide, where 
the motions confpire, rauft prefs and beat the contiguous Air 
more violently than on the other, and there excite a reluftancy 
and reaftion of the Air proportionably greater. And for the fame 
reafoDj if the Rays of light fhould poffibly be globular bodies, 
and by their oblique paffage out of one medium into another ac- 
quire a circulating motion^they ought to feel the greater refiftance 
ftom the ambient iEther, on that fide, where the motions con* 
fpire^ and thence be continually bowed to the other. But not^ 
withftandieg this plaufible ground of fufpitioo 3 when I came to 
examine it, I could obferve no fuch curvity in them. And be- 
fides (which was enough for my purpofe) I obferved, that the 
difference 'twixt the length of the Image, and diameter of the 
hole, through which the light was tranfmitted^was proportionable 
to their diftance* 
The gradual removal of thefefufpitionSsat length led me to the 
ExperimifitumCfrucis^ which was this : I took two boards, and pla- 
ced one of them clofe behind the Prifme at the window , fo that 
thelightmightpafs through a fmall hole, made in it forthepur- 
pofe, and fall on the other boards which I placed at about 12 feet 
diftance, having firft made a fmall hole in it alfo, forlomeof that ' 
Incident light to pafs through. Then I placed another Prifme be* 
ibind this fecond board, fo that the light, trajedied through both 
lihe boards, might pafs through that alfo, and be again refraded 
before it arrived at the wall> This done, I took the firft Prifme in 
my hand , and turned it to and fro flowly about its ^a;^>, fomuc' 
as to make the feveral parts of the ImagCjCafl: on the fecond board, 
iiicctflively pafs through the hole in it , that I might obferve t 
'what places on the wall the fecond Prifme would refrad: them- 
