Philosophical Transactions. 320 



tion of the stars to the south of their predicted places, cannot 

 originate either in the one, or the other — perceiving also that the 

 extent of southern deviation, to which any star was liable, might 

 better be predicted by a reference to its right ascension, than to its 

 declination, Mr. Pond attributes the discordances to some natural 

 cause. He observes, that instruments of well known celebrity, are 

 said to give different results ; claims no superiority for his own 

 catalogue, from the circumstance of its being nearly a mean be- 

 tween those of Dr. Brinkley and Mr. Bessel, but considers each of 

 the latter inaccurate, from flexure of the instruments, with which 

 they were made — and states that his confidence in the accuracy 

 of his present observations, and also in the superiority of the 

 Greenwich circle over all others with the history of which he is 

 acquainted, is derived from the coincidence in the results, obtained 

 by direct and reflected vision, each at the same time giving to the 

 instrument the same horizontal point. 



7. On the Parallax off- Lyra:. By John Pond, Esq., Astronomer Royal. 



The mural circle is here employed, to determine the difference of 

 parallax, between y Draconis and a. Lyrse ; and also the absolute 

 parallax of the latter star— every care was taken, to equalize the 

 temperature of the observatory with that of the outer air, and so 

 nearly was this effected, that it became a matter of indifference, 

 whether the observations were reduced by the employment of the 

 interior or exterior thermometer — and the same results were 

 obtained, whether two or six microscopes were used ; (a circum- 

 stance strongly proving, that no cause of error need be expected 

 from partial expansions of the limb of the instrument;) namely, 

 that the angular distance between the two stars, measured in 

 summer and winter, does not differ one tenth of a second — hence 

 7 Draconis and a. Lyrae have the same parallax, or their difference 

 of parallax is = o. 



Absolute Parallax of a. Lyroe. 



The observations to determine this, were made by reflection as 

 well as by direct vision; equal pains were again taken to equalize 

 the temperature of the inner with the outer air, and with the same 

 success ; the same results were procured, whether two or six 

 microscopes were employed. They indicate that the sensible 

 parallax of a Lyrse, cannot exceed a very small fraction of a second. 

 The reason why Dr. Brinkley finds no parallax in y Draconis, a 

 small quantity in « Cygni, more in «. Lyrse, &c, Mr. Pond attributes 

 to the nature of his instrument, which as far as the zenith point is 

 concerned, may be considered perfect, but which in proportion, as 

 it is directed from the zenith, becomes less and less perfect. 

 Mr. Pond concludes the paper thus : " The history of annual 



