"64 ESSAYS anp OBSERVATIONS 
derable length. Difcoveries of this kind 
are capable of a particular fort of proof, 
which is very beautiful and convincing, 
from the exact concidence of the compu- 
ted effects with the real ones, as to quan-: 
tity. Many inftances of this occur in 
Sir Ifaac Newton’s writings, and in all 
mathematical philofophy : fuch as the cal- 
culation of the moan’s irregularities; of 
the tides; of the preceflion of the equinoxes; 
of the refiftance of fiuids ; and, in optics, 
his computation of the dimenfions of the 
rainbow ; of the aberration of colours; of 
the intervals of the fits of reflexion and 
tranfimiffion ; and of the coloured rings 
reflected by thick tranfparent /peculums, 
Wart farther I have to offer concern- 
Jight and colours, confifting chiefly of 
doubts, difficulties, or loofe conjectures, 
thall be propofed under the form of ques 
TICS. 
SECT, 
