greater, he might have made the length not oa!y five, but fix or 
eight times the breadth and more. No wonder therefore, that 
Mr*L»f^ found the Image flioner than I did , feeing he tried 
the Experiment with a lefs Angle. 
The Angle indeed which I ufed was but about 63 degrees 
12 minutes, and his is fee down 60 degrees 5 the difference of 
which from mine,being but 3 degrees 1 z minutes, is too little to 
reconcile us, but yet it will bring us confiderably nearer to* 
geihen And if his Angle was not exadly meafured , but the 
round number of 60 degrees fet down byguefs or by a lefs 
accurate meafure (as I fufpeft by the con;e6ural meafureof 
therefraflion of his Prifm by the mio of thefigns 2 to 35fec 
down at thefame time, infteadof an Experimental one^) then 
might it be two or three degrees lefs than 60, if not ftill lefs : 
and all this, if it fliouldbe fa, would take away the greateft 
part of the difference between us. 
But however it be, I am well affured^my own obfervation 
was exaft enough. For I have repeated it divers times fince 
the receipt of Mr^ L»r^'s Letter, and that without any con* 
fiderable difference of my Obfervations either from one ano* 
ther,-or from what I wrote before. And that it might appear 
experimentally, how the increafe of the Angle incrcafes the 
length of the Image, and alfo that no body who has a mind to 
try the Experiment exaftiy, might be troubled to procure a 
Prifin which has an angle juft of the bignefs aillgned by me; I 
tried the Experiment with divers Angles, and have fet down 
my Trialsin the following Table; where the firft column ex- 
preiTes the fix Angles of two Prifms which I 13 fed, which 
were meafured as exafily as 1 could by apply ing them to the 
angle of aSedior; and the fecond column expreffes in inches 
thelength of the Image made by each of thofe Angles ; its 
breadth being two inchesj its diflance from thePrifo) 18 feee 
and four inches, and the breadth of the hole in the Window- 
fliut \ of an inch. 
^ the jingles of 
degr* min. 
56 I® 
the M Jpfm ' 
the Lengths of 
the Image* 
7i 
loi 
