40:4. Mr. -atwood’s Theory for the Mcnfuratlon 
ED : through I and F draw the arc IF : then the given arc 
KF or KI, and the- angle IKP, meafured by the given arc PQ, 
define the triangle 1 KF, and in it, therefore, the fide IF and 
and tiie angle IFK. are determined. If from IFK, the given 
angle DPK, meafured by the arc XY, be fubtradfed, the re- 
mainder IFD, and IFB its fupplement to 180° will be defined.: 
the given arc FB, with the angle IFB and the arc IF, deter- 
mine the angle IBF, and the arc IB, or its double BE .: and the 
given arc BD, the arc BE, with the contained angle DBE before 
determined, define the arc ED, which is therefore the true mea- 
fure of the angle fubtended by the objects obferved under the 
conditions fulfilled in the. conifruftiom 
7. The computation of the obferved angle DCE being for 
the prefent omitted, fome confequences which follow from the 
conftrudtion may be inferted in this place, being either corol- 
laries, or fuck truths as admit of eafiy geometrical deduction 
from the general propofition. The line DC will always be the 
pofition of the vifiual ray or line of collimation of the telefcope 
ufied in the obfiervation, and the inclination of it to the plane 
of motion will be meafured by the complement of the arc DK 
to a quadrant. The line BC will be the pofition of the ray 
which pafies between the refledtors B and C, and the inclina- 
tion of it to the plane of motion will be meafured by the com- 
plement of the arc BK to a quadrant. Thefie arcs are left out 
■of the figure, that the more material parts of the confiradtion 
might not beconfufied by them. 
8. Every thing elfie remaining, let the parallel FIM (fig. 3.) 
he projedted on the plane of motion QOP. Through the 
points F and I draw the arc of a great circle NIFR. The ob- 
fei-ved * objedts T and S, or, which is the fame thing, the points 
.of i nter fedtion at the fphere’s furface E and D will be at equal 
-■* Compare fig. 2. 
perpen- 
