Bond, Graham, and Peirce, on the Latitude of Cambridge. 187 
its transits over one of the wires, when this wire is north of the axis 
of collimation. But when the axis of the telescope is reversed, so 
as to bring this wire south of the axis of collimation, B and B’ are 
the points of east and west transit. 
Let 
h,=APZ=3 (APM) 
= } the sidereal interval between the times of east and west transit, 
when the wire is north of the axis of collimation. 
h, = BP Z = 3 the sidereal interval, when the wire is south of the axis 
of collimation. 
ASA is the arc of a great circle joining 4 and 7%. 
BS’ B’ is the arc of a great circle joining B and B’. 
Each of these circles is perpendicular to P Z.M. 
Let D = the star’s declination. 
L,,= the declination of the point S. 
L, = the declination of the point S’. 
The right triangles PS and BPS give the following formule 
for determining Z,, and L,: — 
