222 



the variable force of wind upon its velocity, and state their mode of 

 annihilating such cause of error. They then detail their own expe- 

 riments, for which they selected two open and elevated spots in the 

 plains of Utrecht, distinctly visible from each other, and distant about 

 9664 fathoms. They measured the interval between seeing the light 

 and hearing the sound by clocks with conical pendulums, which di- 

 vide the 24 hours into 10,000,000 parts, and one of the indexes of 

 which gives one 1 00th part of a decimal second. Each station was also 

 furnished with a good barometer, several accurate thermometers and 

 excellent telescopes, and the humidity of the air was determined by 

 Daniell's hygrometer. The authors then describe the means which 

 they adopted to insure the simultaneous firing of shots at both sta- 

 tions, and by which they succeeded in bringing them within 1" 

 or 2" of each other, and enter at considerable length into the details 

 of their different experiments, the results of which are given in se- 

 veral tables annexed to this paper; among which will be found one 

 exhibiting a general view of the results of the experiments of those 

 different philosophers who have investigated this subject. 



In conclusion, it appears from their researches that at the tempe- 

 rature of 32, the velocity of sound is 1089*7445 English feet per 

 sexagesimal second. 



A Catalogue of nearly all the principal fixed Stars between the Zenith 

 of Cape Town, Cape of Good Hope, and the South Pole, reduced to 

 the 1st of January, 1824. By the Reverend Fearon Fallows, M.A. 

 F.R.S. Read February 26, 1824. [Phil. Trans. 1824, p. 457.] 



Remarks on the Parallax of a. Lyra. By J. Brinkley, D.D. F.R.S. fyc. 

 Andrews Professor of Astronomy in the University of Dublin. 

 Read March 11, 1824. \Phil. Trans. 1824,;?. 471.] 



The author's object in this paper is principally to form a correct 

 estimate of the absolute and relative degrees of accuracy of the in- 

 struments at Dublin and at Greenwich. He first considers the dif- 

 ference of parallax between y Draconis and a Lyrae, and secondly, 

 the absolute parallax of a Lyrae. 



He exhibits, hi a table, the whole of the results of 337 observations 

 of Mr. Pond for the intercepted arc, reduced to the 1st of January 

 1815, chiefly by Mr. Pond's own computations. From 46 observations 

 made in the year 1812, he deduces 0"'28 for the coefficient of the 

 effect of parallax ; and from such of his observations as were made 

 in the same day, the number deduced is 0"'54. 



In 1813 there is a difference of half a second between the mean of 

 22 observations in June and July, and of 17 in August; hence Dr. 

 Brinkley was led to examine the observations of this year alone, and 

 he found that 61 of them, from June to December, as reduced by 

 Mr. Pond, gave 0"*42 for the coefficient of parallax ; and omitting 

 the last five days of observation 0"'89, which is little less than the 

 result of his own researches. 



