On a New Method of recording differences of Declination. 3 
In case a known catalogue is under review, the amount of 
work done during the night will depend solely on the rapidity 
with which the finders of the telescope can be set. If we allow 
for each star three minutes, (which with an assistant to set has 
been found suflicient,) we have without difficulty 200 observa- 
tions on twenty different objects within the hour, and for a night’s 
work of five hours, one thousand wires or observations record 
on one hundred stars or other objects. If however the work 
done is independent of any catalogue, and we are sweeping the 
heavens it zones, there is no difficulty in recording both R. A. and 
declination on single wires just as rapidly as the stars see 
themselves, even up to 300 stars per hour of time. This 
actually been done. For the purpose therefore of cataloguing the 
heavens, the new methods offer advantages of the highest im- 
portance. 
We now present some of the results tending to demonstrate 
the degree of precision already reached in the determination of 
differences of declination. As the whole subject was a 
new, no advantage could be gained from the experience of o 
observatories, and hence’ the difficulties which have been ronal 
Were encountered tinder the most unfavorable eral yet 
Having however implicit confidence in the grea in- 
volved in the new machinery, I never doubted $e a moment that 
the discrepancies which arose would finally be cn to mechan- 
ical defects, or to accidental and unanticipated ca 
My attention has been exclusively directed to this single point. 
vine what a wh re error could the new = 150 roid repeat its 
ifferen 
ticabilit 
In my very earliest obsdevutions with fen declination wires, 
more than two and a half years’since, a simple inspection of the 
record in the shape of ten delicate wedged-shaped dots on metal, 
with a powerful microscope, demonstrated at once the perfection 
with which these records were made within the narrow space oc- 
cupied by these ten dots. The wires were as nearly parallel and 
ho mg as we could place them. Yet the small inequalities 
of distance were always measured with a precision only limited 
by the power of bisection under the circumstances existing dur- 
i the observation. When the weather was tranquil and the 
stars steady, the most admirably accordant results were reached : 
calmly when the stars were dancing ot ill-defined, dis- 
poe ec ear were recorded, doubtless due to errors of bisection. 
pe 2 4 ont eae st 
