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lumns which had not yet pafs’d the Line C D, were 
more numerous and more remote from it than thole 
which had pals’d it ; for if the Point E, be farther 
diftant from C D than the Point F, the Arch A e, 
mull needs be lefs than the Arch B f. An irregular 
gull of Wind blowing upon and lhaking the Columns, 
was (I fuppofej the Caufe of that trembling, which 
appear’d in the triangular Streams, and the Caufe al- 
fo which deftroy’d that fine appearance of the Cano- 
py. The (lender circular waves feen at the fame time 
might alfo be explain’d from the fame Caufe. I need 
not detain you any longer by endeavouring to make 
outfome other particulars of thisunufual Appearance: I 
fear l have been already too tedious. However l wiU 
not omit to mention a very eafy Contrivance by which 
the Thing maybe tolerably well reprefented to view. 
Take a Hoop and round about it fallen feveral (freight 
Sticks parallel to each other, but all inclin’d to the 
plane of the Hoop, hold this plane parallel to the Ho- 
rizon, and in that pofture move it with Sticks over 
a Candle, the fhadows of the Sticks upon the Cei- 
ling of your Room, will converge to a point not di* 
re&ly over the Candle, (as they would have done, had 
the Sticks been perpendicular to the plane of the Hoop) 
but to the Point in which a Line drawn from the 
Candle parallel to the Sticks, (hall interfedt the plane 
of the Ceiling. 
IV. A 
