Report of ihe Ailronomical Society. 279 



respect to the three following fixed stars, which are situated near 

 the path of his orbit, and whose mean places for the day of op- 

 positiou are here stated : viz. 



When Mars approaches either of these stars, the differences in 

 right ascension and declination, between the planet and the star, 

 must be taken as accurately as possible for several successive days, 

 with a micrometer ; or their distances measured, in a straight 

 line : the time and place being correctly noted down. Such ob- 

 servations, compared with corresponding ones made in England, 

 will serve to determine the parallax of Mars. 



With the same view it was proposed to Captain Hal!, to make 

 observations on Venu"-, at the time of her inferior conjunction in 

 March 1822, by comparing her with a Ceti, on the parallel of 

 which she will be a day or two before and after the conjunction: 

 a simple and easy method being at the same time suggested, 

 whereby Venus might be readily found in the day time, notwith- 

 standing her proximity to the sun. 



The attention of Captain Hall was also directed to the subject 

 of refraction, in order to determine whether the quantity of re- 

 fraction varies (cufteris parilns) in different parts of the globe ; 

 or whether any new light can be thrown on this uncertain phae- 

 nomenon, in tlie various places he nsight visit. 



Upon most of these subjects, it must be evident to the mem- 

 bers of the Society, tluit there is a necessity of having correspond- 

 ing and simultaneous observations in this country: otherwise the 

 labours of Captain Hall (should he be favourablv situated for ob- 

 servation) will be in a great measure lost to the public. Those 

 members, therefore, who possess the requisite instruments, are 

 called upon to co-operate on these points, and to register their 

 observations, in order that they may be compared at a future op- 

 portunity. Without this assistance the efforts of the Council will 

 have been exerted in vain, and the time of an active observer 

 employed to little or no advantage. And here the Council can- 

 not avoid suggesting, to those astroiunners who possess the re- 

 quisite instruments, the projuicty of observing and recording the 

 position (in right ascension ami declinntiun) of those stars which 

 are situated near to, and on the same parallel with, any of the 

 planets near the time of their opposition ; since such observations 



would 



