SOUTHERN ASTRONOMERS and
AUSTRALIAN ASTRONOMY

INTRODUCTION to DUNLOP’S
DOUBLE STAR CATALOGUE

XVII. Approximate Places of Double Stars
in the Southern Hemisphere, observed at Parramatta 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^o, 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

The DUNLOP PAIRS

By Andrew James

Current Available On-Line Written Text

Last Update : 12 February 2005

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