SOUTHERN ASTRONOMERS and
AUSTRALIAN ASTRONOMY
DUNLOP’S DOUBLE STAR
CATALOGUE
XVII. Approximate Places of Double Stars in the
Southern Hemisphere, observed at Paramatta
in New South
Wales.
By JAMES DUNLOP, Esq.
In a Letter addressed to Sir T. MACDOUGAL BRISBANE, K.C.B.
&c.
Read May 9, 1828
SIR,
IN presenting this list of double stars, it may be
necessary for me to make some apology for its imperfect state, as
regards the true apparent distance and position of a great many
double stars, the situation of which points out in the heavens.
You are aware that during your administration of the
government of the colony of New South Wales, my time and attention
were wholly devoted, in your employ, to the Parramatta observatory in
the miscellaneous observations which occurred; and principally in
observing the right ascensions and polar distances of the fixed
stars, thereby collecting materials towards the formation of a
catalogue of stars in that hemisphere (which materials have been
presented by you to the Royal Society in London) : and your departure
from the colony alone prevented me from pursuing that branch
further.
Finding myself in possession of reflecting telescopes,
which I consider capable of adding considerable knowledge of the
nebulæ and double stars in that portion
of the heavens, I
resolved to remain behind to prosecute my favourite pursuits, in
collecting materials toward the formation of a catalogue of
nebulæ and double stars in that hemisphere, and any other
object that may attract my attention.
The nebulæ being a primary object to me,
I
devoted the whole of the favourable weather in the absence
of the
moon to that department, and moonlight, in general, was allotted of
the observations of double stars ; a portion only of which I have
been able to subject to the various measurements necessary for the
accurate determinations of the relative distances and positions.
In the case of the stars marked with an asterisk,
their positions, distances, declinations, &c., are the results of
micrometrical measurements with the 46-inch achromatic telescope
mounted on the equatorial stand which you left me : the micrometers
were constructed by myself, consisting of a parallel line micrometer,
the screws of which I bestowed great pains upon, and which I consider
very excellent and uniform ; also a double image micrometer on
AMICI’S principle, which I sometimes
used, particularly when the stars were nearly of equal magnitudes (I
always found some uncertainty in the measurements, when the stars
were of very unequal magnitudes) : the position micrometer was made
by BANCKS, and belong to the telescope.
In the case of those stars which are not
marked with
an asterisk, their positions and distances were only estimations
while passing through the field of the 9-feet telescope : in the
various sweeps, the AR and declinations are also those which were
indicated by the same instrument fitted up and described as a
meridian telescope, in my paper on the nebulae in the southern
hemisphere.
I will only extend at length the observations
of a
few of the principal stats, merely to show the manner in which they
have been conducted : the value of one revolution of the line
micrometer is equal to 58″,051 ; the circular head of the
micrometer is divided into 120 divisions, and each division estimated
to tenths ; the value of fifty divisions on the scale of the double
image micrometer is equal to 18″,75, and one revolution of the
position micrometer equal to 24°, which was subdivided into
sixty parts equal to 24′ each.
Trusting that my humble efforts will be of some
service to science,
I have the honour to be, Sir,
Your obedient Servant,
JAMES DUNLOP
Last Update : 29th January 2014
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