222 Royal Society. 



session of a particular temperature ; both of which probably continue 

 unaltered for periods of indefinite duration, compared with the records 

 of any human history. He considers this phenomenon to be expli- 

 cable, by supposing that a large volume of these gases is pent up in 

 some cavern of rock, at a great depth below the surface of the earth, 

 which, at some former period, had been heated by volcanic action, 

 and which, by the gradual cooling and consequent contraction of its 

 external portions, exerts a continued pressure on the gaseous contents 

 of its cavitv, and determines the uniform flow of a stream of gas 

 through crevices towards the surface. 



It appears from the observations of the author that the quantities 

 of gas disengaged, in a given time, from the King's bath are some- 

 what variable ; for the differences between the results obtained on 

 successive davs are too considerable to be ascribed either to errors 

 of manipulation or to variations in the amount of gas escaping by 

 other avenues. These fluctuations in quantity cannot be traced to 

 have any connexion with those of the atmospheric pressure. Varia- 

 tions likewise were observed in the proportional quantities of carbonic 

 acid contained in the gas evolved at different times, which latter 

 variations the author thinks may perhaps be dependent on the former. 



The author remarks, in conclusion, that the immensity of the volume 

 pf nitrogen gas which is disengaged from these thermal springs, and 

 the entire absence of carburetted, sulphuretted and phosphuretted 

 hydrogen, seems to afford additional presumption against the truth 

 of the opinion that the nitrogen gas which escapes from volcanoes 

 and from these springs is derived from atmospheric air, held in solu- 

 tion by the water, and deprived of the greater part of its oxygen by 

 animal and vegetable putrefaction. He is disposed to ascribe the de- 

 ficiency of oxygen to some process of combustion, during which it 

 unites with some base, forming a compound not easily volatilized by 

 heat; and to account for the presence of carbonic acid, by the calci- 

 nation of earthy carbonates, rather than by the combustion of coal or 

 bitumen. 



" On the Position of the North Magnetic 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 circumstancesof 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 



