C 357 ] 
the focket into fome of the holes, wich were drilled 
in the fupport of the telefcope. 
The polar axis may be fet near enough to the di- 
rection of the meridian, by a magnetic needle, allow- 
ing for the variation ; or, even by the light, pro- 
vided the walls of the obfervatory be built nearly 
north and fouth. This being done, and the direct- 
ing wire being brought into fuch a pofition, that the 
ftar may run exaCtly along it from the centre to 
the extremity of the field of the telefcope ; then if 
the fcrews of the rack work be turned, and the ftar 
be brought back to the interfeCtion of the wires, it 
will be found to run exaCtly along the directing wire 
again ; and this I generally found would be the cafe, 
even for a very confiderable fpace of time, though 
the ftar had, in the mean time, advanced a confi- 
derable way from eaft to weft by the diurnal rota- 
tion ; fo that it is not always neceffary to re-adjuft 
the wires after each fett of obfervations, though it 
may be proper to examine whether they require it 
or not. Hence it follows, .that there can be no 
danger of difturbing the pofition of the wires after 
their adjultment, by bringing the ftar back to the 
entrance of the telefcope, in order to oblerve its 
palfage acrofs all the horary wires. 
Sometimes it fo happens that a proper ftar cannot 
be found that precedes the moon, to compare her 
with ; in fuch a cafe, the obferver muff compare her 
with a ftar following her, and adjuft the wires by 
making fome bright point of the moon run along 
the directing wire, which is a more exaCt method than 
by making the directing wire a tangent to the moon’s 
north 
