Proceedings of Learned Societies. 221 



planet alter. A fluid like water must exist in that part of the sur- 

 face of Mars. Professor Hennessey said that, in controverting an 

 erroneous theory of the earth's figure, he had obtained mathematical 

 expressions for the equilibrium of a fluid like water spread over an 

 exterior abraded spheroid, such as the earth was assumed to be. 

 From these expressions it follows, that if the earth possessed very 

 small ellipticity, it would consist of two circumpolar continents, 

 with an intermediate belt of equatorial ocean ; while, on the con- 

 trary, if the earth had great ellipticity, such as that assumed for 

 Mars, the dry land would form, an equatorial belt, while the poles 

 would be surrounded with water. The attention of observers might 

 be well directed to ascertaining which regions of Mars show the 

 greatest predominance of dry land. Professor Hennessey's own 

 opinion is, that no great amount of equatorial land exists in Mars, 

 and that, therefore, the theory of its comparatively small ellipticity 

 is the more probable. 



On the same day, in the section of Chemical Science, the 

 President, Professor Odling, gave some account of the recent agree- 

 ment among English chemists, as to the combining proportions of 

 the elementary bodies, and the molecular weights of their most 

 important compounds. He said that Berzelius professedly regarded 

 the single combining proportions of hydrogen and chlorine, as con- 

 sisting each of two physical atoms ; but since the two atoms of 

 hydrogen, for instance, which constitute the one combining propor- 

 tion of hydrogen, were chemically inseparable from one another, they 

 were really tantamount to one atom only of hydrogen, and, as a 

 matter of fact, were always employed by Berzelius as representing 

 the single chemical atom of hydrogen, or its smallest actual com- 

 bining proportion. Distinguishing thus, between the physical atom. 

 and the combining proportion, Berzelius' recognition of the truth, 

 that equal volumes of the elementary gases contain an equal 

 number of atoms, was utterly barren. But identifying the physical 

 atom with the combining proportion, Gerhardt's recognition, or 

 rather establishment of the broader truth, that equal volumes of all 

 gases, elementary and compound, contain the same number of atoms, 

 has been in the highest degree prolific. Prom Gerhardt's division 

 of volatile bodies into a majority, whose recognized molecules cor- 

 responded respectively with four volumes of vapour, and a minority, 

 whose recognized molecules correspond respectively with but two 

 volumes, and from his proposals, in conjunction with Laurent, to 

 double the molecular weights of these last, so as to make the mole- 

 cules of all volatile bodies, simple and compound, correspond each 

 with four volumes of vapour, must be traced the development of 

 the matured views on chemical philosophy which now prevail. 

 Professor Odling lamented the unsatisfactory state of chemical 

 notation, and said that Sir B. Brodie was about to publish a plan 

 which would be more suited to the present requirements of chemistry- 

 He referred also to the study of isomerism, which, he said, is the 

 chemical problem of the day, and said that concurrently with its 

 rapidly advancing solution, will be the advance in rational organic 

 synthesis — a subject which, at the present moment, seems to be 

 making comparatively slow progress. 



