I'ts ] 
thereby the rays paffing near the fummit of the 
margin might be fo refracted, as to be thrown upon 
the plain area or bottom. 
Having lately had an opportunity of obferving 
fomething of the fame nature myfelf, I take the 
liberty to lay it before the Society : as alfo to entreat 
their opinion about my conjecture concerning the 
caufe thereof. 
Monday, April 22, 17^1, O. St. being at Marl- 
borough-houfe along with Dr. Stephens and Mr. 
Harris, and having directed the great refleCtor t(> 
the moon, I perceived a tingle ftreak of light pro- 
jected along the flat bottom of the fpot Plato ; and 
from what I was then able to recolleCt of Signor 
Bianchini’s narrative, I could make no doubt but that 
it was of the fame kind with that, which he faw, 
and which I had fo often looked after in vain. By 
the pofition of the fpot on the difk, and the fhadow 
of the mountains on the weft fide of it, we fhould 
not have expeCted to have feen any light on the bot- 
tom. Soon after we difcerned another ftreak of 
light extended along the bottom, parallel to the firft, 
but fomewhat lower, which in a very fliort time 
was evidently divided into- two. I fought in vain 
for fuch a perforation, as that hinted at in the other 
account but thro’ the great magnifying power of 
this inftrument, we were able to difcover a gap or 
notch in the mountains to the weft ward, which abut- 
ted againft the firft ftreak or ftream, and purfuing 
our objeCt with great attention, we alfo perceiv’d a 
like gap in the direction of the lower ftreak : but 
tho’ this ftreak was divided into two, we were not 
able at any ratQ to find out another notch, whereby 
to 
