94 iWr. au Bert’s Method of 
found to come to it, it will be in the proper vertical 
circle. 
The true zenith diftance is found ealily in the follow- 
ing manner; and if diminifhed by the refraction be- 
longing to it, it will give the apparent zenith diftance 
wanted. 
Let hmom repre- 
fent the horizon; z the 
zenith; mm the meri- 
dian ; p the pole of the 
equator ; yy the paral- 
lel of declination of a 
ftar, interfering the 
meridian very near the 
zenith between z and 
p. Then, the vertical 
circles ze on the Eaft- 
ern fide of the meri- 
dian, and zw on the Weftern fide, being drawn to touch 
the path of the ftar, the hour circles palling through the 
points of contaCi e, w, will be at right angles to the circles 
of azimuth ze, zw. 
Now in the right-angled fpheric triangle pez; pz the 
complement of the latitude, and pe the ftar’s polar dif- 
tance, being known, the other parts are ealily found; 
viz, ze the zenith diftance, pze the azimuth, zpe the 
horary angle. So that the telefcope may be fixed pro- 
perly, the pofition of the inftrument is afcertained, and 
the time known when the ftar fnay be expeCted in the 
field 
