with an Equatorial Micrometer. 331 
upon the 23d, the parts 1972, divided by 1.08, gives 1826" 
= 3 q/ 7 ; and the parts of mercury .74, divided by i.o8=r~ 
, ' 6 S // ■= i / 8 // . Now the telefcope being fixed to one point of the 
heavens during the whole period of thefe obfervations, without 
any motion of any of the parts, the fcrews commanding 
the declination wires A and B excepted, we are enabled to 
judge of its fteadinefs to this point by the following remarks. 
If it varied in declination, , this would.be fhewn by the paflage 
of the fame ftar at a different diftance from the center of the 
telefcope at different revolutions ; and if it varied in right afcen-* 
fion, it would be fhewn by its not pafling the horary wires at 
the due time, according to the acceleration of the ftars upon 
the mean time of the. fun.. Both the right afcenfion and de- 
clination may be varied by differences of refraction of the air 
at the fame altitude ; and the right afcenfion is further liable to 
be apparently varied, by the errors of the tranfit inftrument, -the 
tranfit clock, the transferring of its time to the journeyman 
clock, the intermediate errors of the fame, and of the obfer- 
vation itfelf; and as there paffed an interval of. almoft .16 
hours betwixt the paflage of Mercury over the field of. view of 
the telefcope and that of x Ceti, whiclx was the nearefl: flar 
wherewith a comparifon could be made, it will be a fatisfac- 
tion to fee, as before intimated, what variations arofe in flill 
greater intervals of time. 
In right afcenfion.- 
, „ 
Thus \ Ceti upon Sept. 23. paffed the horary wires at • - 9 II 28.3 
an 4 — 26. • S 59 40*6 
\ Ceti therefore came fooner in three days by' - 
but - ought to accelerate on mean time - ~ 
therefore came after three days exadly to the time. 
11 47-7 
11 47.7 
Again* 
