302 Analyses of Books'. I [April* 



account the inaccuracies that are owing to the neglect of 

 moisture diffused in the atmosphere, or to our want of an exact 

 knowledge of the law of density in regard to temperature. There 

 can hardly be any other remedy than that of which astronomers 

 so often avail themselves, whenever an ignorance of the real 

 causes obliges them to assimilate the phenomena to the effect of 

 chance ; namely, to multiply observations in different circum- 

 stances, with the view of making the inequalities of an opposite 

 description compensate one another. 



From the foregoing discussion we may draw this conclusion : 

 that an atmosphere constituted like that of the earth must have 

 an altitude of at least 25 miles in order that the refractions from 

 the zenith to the horizon be such as they are actually observed 

 to be But an atmosphere agreeing with nature in the quantity of 

 the refractions may be found, that shall have any proposed alti- 

 tude greater than the minimum quantity ; and we may infer from 

 the duration of twilight, that the atmosphere of the earth must 

 have an altitude equal to 50 miles, or even more. 



XXIX. Observations on Air found in the Pleura, in a Case of 

 Pneumato-thorax ; tvith Experiments on the Absorption of different 

 Kinds of Air introduced into the Pleura. By John Davy, MD. 



FRS. 



A brief abstract of this paper will be found in our report of the 

 proceedings of the Royal Society, in the Annals for July, 1823. 

 Dr. Davy has added, in an Appendix, an account of a case of 

 pneumato-thorax, in which the operation of tapping the chest 

 was performed ; with some additional observations on air found 

 within the body ; and on the power of mucous membranes to 

 absorb air. The air collected in this case, by tapping the chest, 

 consisted of 93 azotic gas, and 7 carbonic acid gas; thus, in 

 composition, proving almost exactly the same as the air found 

 in the fatal case described in the Paper itself. Various facts are 

 adduced, tending to support the idea, that mucous membranes 

 are capable of absorbing air. 



XXX. On Bitumen in Stones. By the Right Hon. George 

 Knox, FRS. 



The results of the experiments detailed by Mr. Knox in this 

 paper, possess considerable interest, particularly as indicating 

 the propriety of instituting further researches on the subject; 

 and of examining stony substances for bitumen when they are 

 submitted to analysis : we therefore subjoin them, in a tabular 

 form. 



