fine of DFO = i — 
tracled leaves n 
of the Angle full 'ended by Two Objedis , &c. 425 
~™~ 9 from which 1 = fin. DOF being fub- 
in 0 
— vXl —tn z . r * * 4 - s X 1 - rn z 
2 ; or became j = - v 9 ?2 = Z — 
Moreover, the * quantity - — - in the nafcent ftate of i — / and 
i _ n — — and — ■ ■■■ . Making therefore in the 
i-w 2 * 4 > i V ! nf 
general exprefiion contained in art. 26. 
— VX I — m 
m 
ax^i-p z =p, and 7 = a = \/j— 4, n = s = i. 
we fihall have 
L of. h D = - 1 6 pax V" i -/?X 1-2/d-f i6p z vx i - 2p z +p z m z =pmpX ^ i-m 2 X ^ i-p 7, 
~\-l6p z vXi-p z -m z + m z p l +mpX . V i -m z x v' l - p z ~ - i6pa X ^ i -p 2 Xi~2p' 1 + 
1 6p z v x 2 - %p z — rn + 2p z m z ^zmp x %/i - m z x : an( j 
becaufe the fine of the obferved angle is 4 p x x 1 - 2/;, 
the error of the obfervation itfelf, that is*. 
ED = 4^ - 
4pv X 2 — 3 p 1 — n z -J- 2p z m' l =P2mpX v ' 1 — m z X ^ 1 — p z \ 
^ 1 -/x 1 - 2 / 
In this example the pofition of the telefcope has been flip* 
pofed exaflly in the plane of motion ; fhould it be in- 
clined to that plane at a fin all angle, of which the verfed 
fine = v, the pofition of the refiedlors and the arc pointed to 
by the index, being correct, the general value of cof. "ED will 
give the error of the obfervation* or ED — —AP vXs/ l ~P 
1 — 2 f 
t- 
30. To 
* The. nafcent value of 1 — i_ zzz- ;.but = — — 
1 — n __ 
2WI 
m 
m 
1 s z u z 
wherefore = when 5 and n are nearly zr 1. 
1— n 1 —m 
4 When the pofition of the telefcope only is erroneous* the points F and O 
coincide.: 
