Mr Dunlop'*s Jpproa^imate places, 4*c. 301 



refractive and dispersive powers of the materials which he 

 means to employ. 



From these observations we have no hesitation in conclud- 

 ing, that the existing tables of refractive and dispersive powers, 

 with all their imperfections and errors, are of great use in sci- 

 entific researches. If they do not afford scientific data on 

 which the philosopher may confidently rest, they furnish him 

 with approximate results, and general indications; and are per-~ 

 haps the more valuable to him, that they compel him to as- 

 certain the properties of the materials themselves with which 

 he works, or about which he reasons. 



Now that mineralogy depends in a very great degree on the 

 determination of the physical characters of the bodies which 

 it embraces, we are on this account anxious to see new tableis 

 of refractive and dispersive powers ; and we would strongly re- 

 commend the subject as one that would establish the reputa- 

 tion of any young philosopher who has the courage to devote 

 himself to so laborious a task. 



Art. XVI. — Approximate Places of Double Stars in the 

 Southern Hemisphere observed at Paramatta in New South 

 Wales. * By James Dunlop, Esq. In a Letter to Sir T. 

 Macdougal BuisBANE, K. C. B., F. R. S. Lend, and Ed. 



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 of the dou- 

 ble stars, the situation of which it points out in the heavens. 



You are aware that during your administration of the govern- 

 Jpfimt of the colony of New South Wales, my time and attention 

 were wholly devoted, in your employ, to the Paramatta observa- 

 tory 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 for^ 

 BQation of a catalogue of stars in that hemisphere (which mate- 



* Abridged from the Transactions of the Astronomical Society of Lon- 

 don. Read May 9, 1828. 



