( ) 
Angle under L K V is equal to twice the Complement 
to a right Angle of the Angle under KX V, which is 
equal to the Angle of Incidence, and exceeds the re* 
framed Angle by the Angle under A K L. 
’ The Determinations of thefe two Propofitions, 
have relation to the lirft and lecond Rainbow ; thole 
of the firlt Propofition relpe(Sling the interior, and thole 
of the fecond the exterior. The firll Determinations 
of thefe two Propofitions alTign the Angles, under 
which each Rainbow will appear in any given refrad:- 
ing Power of the tranlparent Subltance, by which they 
are produced ; the latter Determinations of thele Pro- 
pofitions teach how to find the refrading Power of the 
Subfiance, from the Angles under which the Rain- 
bows appear ; the Angle under C M G, in the Deter- 
minations of the firft Propofition, being half the Angle 
which mealures the Diftance of the interior Bow from 
the Point oppofite to the Sun ; and in the Determi- 
nations of the fecond Propofition, the Angle under 
CMN is half the Complement to aright Angle of 
half the Angle that mealures the Diftance of the exterior 
Bow, from the Point oppofite to the Sun. But where- 
as thefe latter Determinations require Iblid Geometry, 
it may not be amifs here to lliew how they may be 
reduced to Calculation, feeing the Oblervation of thele 
Angles, as the learned T>t. Halley has already re- 
mark’d % afibrds no inconvenient Method of find- 
ing the refrading Power of any Fluid, or indeed of any 
tranlparent Subftance, if it be formed into a Iphericd 
» J^hilofoph, Tranfa£l. No. 267. 722, 
or 
