291 



J* concerned, give results perfectly identical, as he shows by actual 

 comparison of his own final numbers. 



The second series of experiments were made at Port Bowen, where 

 the ships of the North WesternExpedition wintered from 1824 to 1825. 

 The observatory was erected near the harbour, 100 feet above the sea, 

 on secondary limestone, on a hard frozen soil, and the locality is very 

 minutely described. The apartment in which the observations were 

 conducted was thickly lined with fearnaught cloth. At first it was 

 attempted to warm it by a stove ; but the fluctuations of temperature 

 so produced proved too great, and the stove was therefore removed 

 outside, and the observatory warmed by the smoke-pipe ; while the 

 whole apparatus was fenced from draughts of air and sudden change 

 of temperature by a large envelope of fearnaught lined with racoon 

 skins. These precautions proved so effectual, that the total change 

 of temperature during the observation was seldom more than 3, and 

 frequently not 1, from 50 ; while by a Six's self-registering ther- 

 mometer, the mean range of temperature, in 24 hours, to which the 

 pendulum was exposed, was only 8, and the extreme 12 ; while 

 that of the atmosphere varied from 23 to 47 irregularly. 



During the whole of these observations, every precaution was used 

 to secure and examine the stability of the whole apparatus, and that 

 with perfect success. The time was determined by transits of the 

 sun, Arcturus, and a Lyrse. The clock was one belonging to the 

 Royal Society, fitted with a gridiron pendulum, suspended on knife 

 edges. The transit instrument was of 30 inches focus and 2 inches 

 aperture, cemented by plaster of Paris to a large stone placed on a 

 cask full of sand. 



A second distinct series of observations, under very favourable 

 circumstances of weather, was made in July, the results of which 

 differ only one tenth of a vibration in 24 hours from those in June ; 

 and a mean of both, according to the number of factors in each se- 

 ries, gives the number of vibrations for Port Bowen. 



The third experiment was made at Greenwich, on the return of the 

 Expedition in November, 1825. The number of vibrations in 24 

 hours derived from it, differed 0'24 of a vibration from that con- 

 cluded from the first experiment, and this difference was maintained 

 on repetition. The author attributes this to wear of the knife edges, 

 a fine line of metal being visible on the agate planes supporting them. 

 Supposing this wear uniform, the author takes the mean of the two 

 determinations to compare with that at Port Bowen. 



He concludes his introduction by a justly merited acknowledge- 

 ment of the efficient cooperation afforded by the commander of the 

 Expedition throughout the whole of these researches. 



The remainder of this communication consists of an ample and 

 very minute and regular detail of the series of observations. They 

 commence with the first experiments at Greenwich, which continued 

 from the 20th to the 25th of April, 1824. The time here has been 

 deduced by comparison of the pendulum clock with that of the transit 

 room of the Observatory. A table Is given of these comparisons, regu- 



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