EKpcruuent hetryed,by letting the Sun-beains through a Httle hole 
into 4 darkchamberjwhich palTing through a glafs Prifm to the op- 
pofitewall, exbibited there a of divers colours, but in a 
form much morfelbngt hep broad: whereas according to the receiv- 
ed Laws of Refradion, it flbould rather have appeared in a circular 
form.Whcreupon conceiving a defed in thofe ufual Laws of Refra- 
dion, he frames his new Tb^Qify.of Light, giving to feveral rays,fe- 
v^ral rcfrjLDgibilUie», v^ithout refpcd to their Angles of Inci- 
TruLy ,Sir J cJbdi^t nat of what this learned Author here affirms ; 
and have my felf fometimes inlike circumftances obferved the like 
difference between the length and breadth of this coloured iS/^- 
Brum \ but never found it fo when the sky was clear and free from 
clouds,near the Sumbut then only appeared thisdifferenceof length 
and breadth, when the Sun either fljined through a white cloud, or 
enlighcned fome fuch clouds near unto it. And then indeed it was no 
marvel, the faid 5]p^(Sr;^ fliouId be longer then broad ; fincethe 
cloud or ciQuds,Xo;enlrghtned, were in order to thofe colours like 
to a great Sun^makitig a far greater Angle of Interfedion in t he fald 
ho!e,then the true rays of the Sun do make; and therefore are able to 
enlighten the whole length of the Prifm,and not only fome fmall part 
thereof,as we fee enlightned by the true Sun-beams coming through 
the fame little hole. And this we behold alfo in the true Sun-beams, 
when they enlighten the whole Prifm;for,al though in a clear Heaven, 
the rays of the Sun^paffing through the faid hole^never make a Spe^ 
itrumlovi^v then broad,becaufe they then occupy but a fmall part 
of the Prifm 5 yet if the hole be fo much bigger as to enlighten the 
-whole Prifm, you fliall prefently fee the length of the SpeSirum 
much exceed its breadthj which excefs will bealwaysfo much the 
greater ,as the length of the Prifm exceeds its breadth* From whence 
I conclude, that the Spe£irum,\\\\s learned Author favv much longer 
then broad, was not effeded by the true Sun-beams, but by rays 
proceeding from fome bright cloud,as is faid-and by confequence, 
that the Theory of Light grounded upon that Experiment cannot 
fabfift. . ^ 
What I have here faid,needs no other confirmation than meer ex- 
perience,which any one may quickly try; neither have I only tryed 
the fame upon this occafion,but near 30 years ago fliewed the fame, 
together with divers other Experiments^ of Light, to that worthy 
Promoter of Experiiiiental Philofophy, Sr. KenelmDigby, who 
comitig into thefe part3 to cake the Spaw Waters, reforted oftentimes 
to 
