. 1 823.] Philosophical Transactions for 1 823, Part I. 22*7 



would occupy a far greater space than we could at present 

 devote to the subject : we must, therefore, confine our extracts, 

 in this place, to the conclusion of the paper on the parallax of 

 a Lyrae ; the difterence between which and that of y Draconis, 

 Mr. Pond finds, is absolutely a quantity too small to be mea- 

 sured, or it is zero ; and his observations indicate, in the most 

 decided manner, that the actual parallax of the former star can- 

 not exceed a very small fraction of a second. 



" Notwithstanding the importance of these investigations to 

 the history of astronomy, and to our forming a correct notion of 

 the system of the universe, yet our decision ultimately turns 

 upon so very small a quantity, that our having reduced the 

 inquiry to these narrow limits, rather tends to show the perfec- 

 tion of each instrument [of Greenwich, and of Dublin], than the 

 defect of either." 



" On former occasions, I considered the question of parallax 

 in the particular case of cc Lyree as undecided, and as perfectly 

 open to future investigation ; but the observations of the present 

 year have produced, on my mind, a conviction approaching to 

 moral certainty. The history of annual parallax appears to me 

 to be this : in proportion as instruments have been imperfect iu 

 their construction, they have misled observers into the belief of 

 the existence of sensible parallax. This has happened in Italy 

 to astronomers of the very first reputation. The Dublin instru- 

 ment is superior to any of a similar construction on the Conti- 

 nent ; and, accordingly, it shows a much less parallax than the 

 Italian astronomers imagined they had detected. Conceiving 

 that I have established, beyond a doubt, that the Greenwich 

 instrument approaches still nearer to perfection, I can come to 

 no other conclusion than that this is the reason why it discovers 

 no parallax at all." 



VIII. Observations on the Heights of Places in the Trigonome- 

 trical Survey of Great Britainy and upon the Latitude of Arhury 

 Hill. By B. Bevan, Esq. : Communicated by Sir H. Davy, 

 Bart. PRS. 



By means of levelling to the canals, &c. Mr. Bevan found the 

 country to the north of Arbury Hill suddenly to fall about 400 

 feet, and continue at this depressed state for nine or ten miles. 

 This " defect of matter," he observes, ''was a strong ground for 

 supposing a deflection of the plumb-line to the southward;" and 

 by calculating the latitude of Arbury station, from the latitude 

 of Blenheim, as determined by previous observation, independent 

 of any astronomical observation made at Arbury, he found it to 

 be 52° 13' 23^', or five seconds less than was shown by the zenith 

 sector. For the calculation by which this discrepancy was de- 

 duced, and for the other subjects of the paper, we must refer the 

 reader to the original. B. 



{To be continued.) 



Q'2 



