254 



of the moon and of the planets, and also in that of a greater rapidity 

 of approximation by the improvements introduced in these methods. 



Laplace, in the Mecanique Celeste, alludes to an equation of long 

 period, of which the argument is twice the longitude of the moon's 

 node, plus the longitude of her perigee, minus three times the longi- 

 tude of the sun's perigee ; and M. Poisson has shown that the co- 

 efficient of the corresponding argument in the development of the 

 disturbing function equals zero : but the author shows that the same 

 result may be arrived at very simply, by means of the method of de- 

 veloping the variation of the disturbing function. 



December 19, 1833. 

 MARK ISAMBARD BRUNEL, Esq., Vice-President, in the Chair. 



A paper was read, entitled, " On the Position of the North Mag - 

 netic Pole." By Commander James Clark Ross, R.N., F.R.S. 



The author remarks that the discordances in former observations 

 made with a view to determine the position of the magnetic pole, 

 have arisen partly from the irregularity of distribution in the earth 

 of the substances which exert magnetic power, and partly from the 

 great distances from the magnetic poles at which these observations 

 have been made. The latter cause of uncertainty has been now, in 

 a great measure, removed, by the numerous and accurate observations 

 made during the late arctic expeditions. The object of the present 

 paper is to put on record those which were made in the last voyage 

 of Captain Ross, in which a spot was reached corresponding to the 

 true north magnetic pole on the surface of the earth. The nature of 

 the instruments, and the difficulties encountered in their practical 

 employment, under the circumstances of theexpedition, are fully stated. 

 Having arrived, on the 1st of June, at north latitude 70° 5' 17'', and 

 west longitude 96° 45' 48", the horizontal magnetic needle exhibited 

 no determinate directive tendency, and the dipping needle was within 

 a minute of the vertical position, a quantity which may be supposed 

 to come within the limits of the errors of observation j hence the 

 author concludes that this spot may be considered as the true mag- 

 netic pole, or as a very near approximation to it, as far, at least, as 

 could be ascertained with the limited means of determination of which 

 he was then in possession. 



A table of the observations, including those on the intensity of the 

 magnetic force at various stations, is subjoined. 



A paper was also read, entitled, " On the Quantity and Quality of 

 the Gases disengaged from the Thermal Spring which supplies the 

 King's Bath, in the City of Bath." By Charles G. B. Daubeny, M.D., 

 F.R.S., Professor of Chemistry in the University of Oxford. 



The author, pursuant to an intention expressed in a former paper 

 read to the Society, undertook a series of experiments, for the purpose 

 of measuring the gas evolved from the thermal springs at Bath during 



