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Experiments to determine the Difference in the Number of Vibrations 

 made by an Invariable Pendulum in the Royal Observatory at Green- 

 wich, and in the House in London in which Captain Kater's Experi- 

 ments were made. By Captain Edward Sabine, of the Royal Artil- 

 lery, Sec. R.S. Communicated by the President and Council. Read 

 December 11, 1828. [Phil Trans. 1829, p. 83.] 



The experiments of which an account is given in tliis paper, were 

 made in compliance with a request of the Council of the Royal Soci- 

 ety, made in December 1827, that Captain Sabine would ascertain the 

 difference in the number of vibrations of a pendulum at Mr. Browne's 

 house, and at the Greenwich Observatory. The author gives a de- 

 scription of the instruments used in the observations ; the first series of 

 which were made in Mr. Browne's house, from the 1 7th to the 20th of 

 March inclusive, and gave as the mean result, 85963*60 vibrations in 

 a mean solar day. A reduction is here introduced, derived from some 

 experiments made on the difference which takes place in the times of 

 vibration in vacuo and in air ; the number of vibrations in the former 

 case being, under the same circumstances as in the observations, 9' 9 7 

 per diem less than in the latter. A corresponding series made at 

 Greenwich in May, gave as the mean 85964*17 vibrations, thus in- 

 dicating an acceleration of 0'57 vibrations per diem; but the differ- 

 ence of latitude and of height between the two stations would have 

 led us from theory to expect a total retardation of 0'38 vibration in 

 the same time. From a second set of observations at Greenwich, the 

 diurnal acceleration appeared to be 0*52 vibration. Taking the mean 

 of this and the former result, it appears that the total amount of the 

 discordance between theory and experiment is 0'91 vibration per 

 diem. The stations are conveniently situated for verifying the ex- 

 istence of this anomaly, and its magnitude is such as to preclude all 

 uncertainty as to its existence. With regard to its cause, the author 

 is confirmed in the opinions he formerly entertained on this subject. 



Tables are subjoined, containing accounts of the rate of the clocks 

 used at both stations, and of the particulars of each series of obser- 

 vations. 



On a definite Arrangement, and Order of the Appearance and Progress, 

 of the Aurora Borealis ; and on its Height above the Surface of the 

 Earth. In a Letter to Davies Gilbert, Esq. M.P. P. R.S. By the 

 Rev. James Farquharson, Minister of the Parish of Allford, Aber- 

 deenshire. Read January 22, and February 29, 1829. [Phil. 

 Trans. 1829, p. 103.] 



The results of the numerous observations of the author on the 

 Aurora Borealis, which on several occasions were made under very 

 favourable circumstances, had already been announced in a short 

 paper, published in 1823 in the Edinburgh Philosophical Journal; 

 and it was concluded from them that the Aurora Borealis has in all 

 cases a determinate arrangement and figure, and follows an invariable 



