152 G E R A R D I R E G N E R I F C K E W S 



« menla ampliora meis; accuraliores subtilioresqiie inscribant divisiones gradiium et mU 

 «nulorum, quam quibus ego ulor ; observaliones insliluant earundcm slellarum , coin- 

 « modissimis aniü tempestalibus, unde veritas ipsis pleno eUtcescet. ( Greuovici ex Obscr» 

 « vatorio Regio Dec. 20, 1698. Johannes Fla msleed.)" 



Sed de Flamsleadio audiamus sentenliam Bradlei ('): 



« The observations of Mr. FJnmsteed of tlie di'Ierent distanoes of the pole star 

 « from Ihe pole at different times of Ihe year, which were through mistake looked 

 « upon by some as a proo of the annual parallai of it, seem been made with mach 

 « ereatcr care than ihose of Dr. Hook. For ihoiigh Ihey do not all exactiy coriespond 

 « with each olher , yet from the whole Mr. Flamsteed concluded Ihat the star was 

 <( 85" 40'' or 45" nearer the pole in December than in May or Jiily: and according to 

 « my hypothesis it ougiit to ni)pear 40" nearer in December than in Jime. The agree- 

 « ment therefore of the observations with the hypothesis is greater than could reasona- 

 « biv be expected , consideriug the radius of tlie instrument , and the manner in which 

 « it was constructed. " 

 et sententiam Brinklei (f) : 



« Flamstcad's insüument , wliich he has described in bis letter to Dr. Wallis, was 

 « a mural arch of 140^, by which he could observe all slars visible in his hemisphere , 

 K and observe below tlie pole all circumpolar stars that were not above ll°f from Ihe 

 « pole. He dedijced tlie index error of his instrument by observations of the pole star 

 « corrected for refraction ; not at first considering any correclion for parallax as neces- 

 « sary : but he soon found a correction necessary , which he attributed to the effect of 

 <( parallax. In this he was singularly mistaken, The lesult of his observations was, 

 « that the diameter of the circle described by the pole star about the pole, was l' 20" , 

 « or r 80" greater in summer Ihaa in winter, This we now know to be the effect of 

 « the aberration oflight. Thus Flamstead's observations give the maximum of aberration 

 «■20" or 22"i. The near argreement of this with liradley's result is much greater than 

 (> -could have been expected from F 1 a m s t e a d'« instrument ; but the remarkable circum- 

 « stance is, that Flamstead should have been so rauch mistaken in his mathematical 

 « application; and that Wallis who interested himself much in the question of pa- 

 « rallax , dit not point out his mistake : it cau only be attributed to the great age of 

 «i Wallis, who was then in his 83"i year." 



(*) Pkil. Trans. ijsS. UV. 66i. 

 (t) Phil. Trans. 1818. 3oi. 



