354 Mi*. Pond on the parallax of the fixed stars. 
Though the method I have adopted in this investigation fe 
extremely simple, I am not aware that it has been ever em- 
ployed before. 1 do not attempt to refer the position of the 
star whose parallax is to be ascertained to any point deter- 
mined by a level or plumb line, but by means of a micro- 
meter within the telescope I measure only its difference of 
declination from some other star which passes through the 
same field ; the telescope itself being securely fixed on a 
stone pier. The star chosen for this purpose should differ 
as much as possible in right ascension from the star whose 
parallax is to be investigated, that the results maybe affected 
by the sum of the parallaxes of both stars. It should like- 
wise be sufficiently bright to be visible even when it passes 
the meridian at noon, otherwise the observations must neces- 
sarily be subject to a period of interruption at the very time 
they would be of the most importance. Should the difference 
of declination of the two stars exceed 8 or 10 minutes, it will 
be advisable to apply a double micrometer to the telescope ; 
that is, a micrometer having two moveable wires, such as 
have been made for some years past by Mr. Troughton, 
and are, I believe, familiar to most astronomers of this 
country.*, 
The star I have selected is /3 Auriga, and the annexed ob- 
servations from Jan. 21st, to May 16th, will show to what a 
very singular degree of precision results may be obtained. 
* As Mr. Troughton’s numerous avocations could not have permitted him to 
satisfy my impatience, which made me very anxious not to lose a season, the instru- 
ment was made by Mr. Doliond. It was executed in great haste (being completed 
in less than three weeks); every part of it, nevertheless, is finished with such care and 
precision, that I regard it as a most valuable acquisition to the Observatory, and 
worthy to hold a place in a collection of instruments, which I believe cannot be 
equalled in Europe. 
