354 



to the plane of the horizon, of the position of a body of determinate 

 figure and weight, when floating on the surface of a fluid. Thus the 

 telescope being attached to a box floating on mercury, and serving 

 as a stand to the telescope, may be fixed either in a horizontal or a 

 vertical position ; in which latter case the reverse observations may 

 be made by merely turning the float half round in azimuth. 



15. The later improvements made by Capt. Kater in the vertical 

 floating collimator are described by him in a subsequent paper pub- 

 lished in the Philosophical Transactions for 1828. Besides ob- 

 viating the sources of error arising from the necessity of transferring 

 the instrument to different sides of the observatory, and of taking the 

 float out of the mercury and replacing it at each observation, the 

 vertical floating collimator has the further advantage of being adapted 

 for use, not only with a circle, but also with a telescope, either of 

 the refracting or reflecting kind. Such a telescope, furnished with 

 a wire micrometer, and directed to the zenith, becomes a zenith 

 telescope, free from all the objections to which the zenith sector, 

 and the ordinary zenith telescopes with a plumb-line, are liable. 

 From the greater degree of precision attainable by the employment 

 of this instnrment, fiom the facility of its construction, the readiness 

 of its application, and the economy of time resulting from its use, the 

 employment of the level and plumb-line may be wholly superseded. 



John Brinkley, Lord Bishop of Cloyne, commenced his scientific 

 career, while Andrews Professor of Astronomy in the University of 

 Dublin, by a mathematical paper published in the Phil. Trans, for 

 1807, containing an investigation of the general term of an important 

 series in the inverse method of finite differences. In 1810 Dr. Mas- 

 keleyne, then Astronomer Royal, announced to the Society by the 

 communication of a letter from Dr. Brinkley, the supposed discovery 

 by the latter of the annual parallax of a Lyrse, which he was confident 

 exceeds 2" . In 1818 he reported having met with apparent motions 

 in several of the fixed stars which he could explain only by referring 

 them to parallax. Among these a Aquilae exhibited the greatest 

 change of place. The observations made at the Greenwich obser- 

 vatory not being in accordance with those made at Dublin, Dr. 

 Brinkley, in a subsequent paper published in the Phil. Trans, for 

 1821, institutes a new series of observations with a view to discover 

 the source of this discordance. In conclusion he states his inabihty 

 to discover any explanation of this difference, or to obtain any result 

 opposed to his former conclusions. He remarks, however, that the 

 discrepancies between his observations and those made at Greenwich 

 may by some be considered as showing the great precision of modern 

 observations, since the whole extent of the absolute difference is 

 only one second. In the last paper on this important subject, which 

 was published in the Phil. Trans, for 1824, Dr. Brinkley endeavours 

 to form a correct estimate of the absolute and relative degrees of 

 accuracy of the instruments at Dublin and at Greenwich. He first 

 considers the difference of parallax between y Draconis and a Lyra?, 

 and secondly the absolute parallax of a Lyrse. 



Four other papers by the same author are also contained in the 

 Philosophical Transactions; the first in 1819, giving the results of 



