Geological Society. 49 



places, consists, at all elevations, of the same (wo gases 

 mixed in the same proportion. This property is equivalent 

 to the law of Mariotte, which is a consequence of it ; for 

 the elastic force in all gases being proportional to the pro- 

 duct of the temperature, density, and a constant which varies 

 with the nature of the gas, the law of Mariotte will hold good 

 in a mixture of two gases, when the volumes of the constituent 

 parts preserve constantly the same proportion. One general 

 law of the constitution of the atmosphere is thus obtained; to 

 which must be added the usual equation of equilibrium. By 

 combining these two properties we deduce a relation between 

 the temperature and pressure at the earth's curface, and the 

 temperature, pressure, and height, at any elevation. But 

 another property is still wanting to complete the development 

 of the constitution of the atmosphere. We must know the 

 law of the decrease of heat in ascending ; of which we are at 

 present entirely ignorant, except the rate of decrease at the 

 earth's surface expressed by the height required to depress 

 the thermometer one degree. Now, from this imperfect ele- 

 ment I have already deduced the barometrical formula in its 

 most improved form; and have computed a table of refrac- 

 tions agreeing with the observed quantities as far as they have 

 been ascertained. My object in the above detail of the chief 

 steps of my investigation, is to enable the unprejudiced in- 

 quirer to judge of its soundness and originality. 



XI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from vol. xix. p. 547-] 

 June 2, "/^N the Faluns of the Loire, and a comparison of their 

 1841. V^ Fossils with those of the newer Tertiary Strata in 

 the Cotentin, and on the relative age of the Faluns and Crag of Suf- 

 folk," by Charles Lyell, Esq., V.P.G.S. 



In a paper " On the Crag of Norfolk and Suffolk," read in 1839*. 

 Mr. Lyell stated, that when M. Desnoyers assigned in 1825 a con- 

 temporaneous origin to the Crag and the Faluns of Touraine, he dis- 

 sented from the conclusion ; first, because the per-centage of recent 

 species then assigned to the crag, including the Norwich beds, was 

 greater than that ascribed by M. Deshayes to the shells of Touraine ; 

 2ndly, because almost all the fossils in each locality were of distinct 

 species, though only 300 miles apart ; and 3rdly, because the fauna 

 of the Suffolk crag had a northern, and that of Touraine an almost 

 tropical a-spect, notwithstanding the geographical proximity of the 



• Proceedings, vol. iii. p. 171. 1839 [Phil. Mag., Third Series, vol. xv. 

 p. 407, 411.— Ed.]. ^ 



Phil. Mag. y. 3. Vol. 20. No. 128. Jan. 1842. E 



