302 Rot/al Society. 



turned to leeward, presents great resistance to lee-way, and very 

 little to going a-head. 



The author then notices the case of a double canoe, or one com- 

 posed of two equal and similar canoes joined together by one com- 

 mon deck, and shows that the same general proposition respecting 

 the conditions of the maximum of stability applies to the double as 

 well as to the single canoe. 



Dec. 1 1. "Experiments to determine the difference in the lengths 



of the seconds pendulum in the Royal Observatory at Greenwich, and 

 in Mr. Browne's house in London, in which Capt. Kater's experi- 

 ments were made," by Capt. E. Sabine, of the Royal Artillery, Sec. 



RS. 



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

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

 Society, in December 1827, that Capt. 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 description 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 859738-38 

 vibrations in a mean solar day. A reduction is here introduced, de- 

 rived from some experiments made on the difference which takes place 

 in the times of vibration in vacuo, and in the air: the number of 

 vibrations in the former case being, under the same circumstances as 

 in the observations, n'62 per diem less than in the latter. A cor- 

 responding series made at Greenwich in May, gave as the mean re- 

 sult 85973-93 vibrations, thus indicating an acceleration of 0-55 

 parts of a vibration per diem. But the differences of latitude and of 

 height between the two stations would have led us from theory to 

 expect a total retardation of 0-38 parts of a vibration in the same 

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

 acceleration appeared to be 0-.'i2 ])arts of a vibration. Taking the 

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

 of the discordance between theory and experiment is 0-9 1 parts of a 

 vibration per diem. The stations are conveniently situated for verify- 

 ing the existence 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 jjarticulars of each series of obser- 

 vations. 



Jan. 8. — A paper was read, intitled, " On the dip of the magne- 

 tic needle in London, in August 1828;" by Capt. Edward Sabine, 

 of the Royal Artillery, Sec. RS. 



This paper commences by noticing, that the Philosophical Trans- 

 actions contain the record of observations on the dip of the needle 

 in London from the early part of the last century to the present 

 time : that these observations all concur in showing a progressive 

 decrease of the dip during the whole i)eriod in question ; but that 



they 



