413 



lie considered that it has been too generally assumed that the 

 boiling point corresponds to a barometric pressure which expresses 

 tlio elasticity of steam taken from the usual tables. He, therefore, 

 attempted to deduce the connection of these data by a direct com- 

 parison of cases, in which both the barometer and boiling point were 

 noticed by himself. He finds this result, that the pressures in- 

 crease riyorously in a geometrical ratio, whilst the temperature of 

 the boiling point rises uniformly. This law is not new, for Deluc 

 arrived at the same result ; but it appears to have been considered 

 by all late writers as unworthy of adoption, and the scale of the 

 elasticities of vapour by Dalton or Ure has been prefen*ed. Now, 

 these elasticities cannot, it is well known, be accurately represented 

 by a geometrical proportion to the temperature ; but Professor Forbes 

 finds that the geometrical ratio represents the barometric heights 

 exactly, whilst the tabular elasticities do not. But, farther, since 

 the common barometric formula shews that the pressure varies geo- 

 metrically, whilst the height above the sea varies uniformly, we 

 have the same form of relation between the boiling point and the 

 barometric pressure as between the height above the sea and the 

 barometric pressure, namely, that each is as the logarithm of the 

 other. Hence the boiling point falls exactly in proportion to the 

 height ascended, and at the rate of 549.5 feet for 1° Fahr. 



The following Donations of Books to the Society's Library 



were announced. 



« 



Monthly Notices of the Astronomical Society of London, containing 

 Abstracts of Papers and Reports of the Proceedings of the So- 

 ciety. Vols. 1, 2, 3, 4, and vol. 5. Nos. 1-27. 



Memoirs of the Royal Astronomical Society. Vol. XIV. — By the 

 Society. 



Examination Papers of the several Faculties in the University of 

 London, for 1842. — By the Council of the University. 



Memoire surla Chaleur des Gas Permanens, par Jean Plana, Astro- 

 nome Royal, et Directeur de I'Observatoire de Turin, — By the 

 Author. 



Journal of the Asiatic Society of Bengal. Nos. 124 and 125, for 

 1842.— Z?y the Society. 



The Quarterly Journal of Agriculture, and the Prize Essays and 

 Transactions of the Highland and Agricultural Society of 

 Scotland. No. 60, for March 1843. 



