SClENTinC NEW*. ' 401. 



On the one hand we obserte the geometer assuming as 

 data the facts observed in the cabinet of an experimental 

 philosopher deduces a rule for measuring the heights of 

 mountains ; and on the other, an observer assuming for 

 his basis of deduction the known height of a mountain, 

 and the effect which it produces upon the elevation of the 

 mercurial column in the barometer, draws his conclusion 

 as to the relative weights of mercury and of air, and 

 finds the same quantities which were made use of by the 

 geometer for establishing his calculations. These com- 

 parisons, which become every day more numerous in the 

 application of analysis; these identical results obtained 

 by processes so contrary, and deduced from phenomena 

 so different, are proofs which establish ike sciences be- 

 yond all question. 



This important result does not constitute th€ only merit Circumstance* 

 of M. Raymond's memoir. Methods of distinguishing necessary to 

 , , . \ . ^ r 11 X • • • 1 X be attended to 



the Circumstances most favourable or most mimical to ^j^i^^j.q^^^j.i^j^ 



this description of observations, are pointed out and ar- observations, 

 ranged under three different titles,— The influence of the 

 time of day, of the stations, and of the meteors. As to 

 the time of day, it is found that the heights observed in 

 the morning and the evening are always too small ; whence 

 it follows that observations ought always to be made 

 about the middle of the day, which is a condition very 

 easy to be complied with. The influence of stations is 

 not less real, but more difficult to be obviated. The 

 rule to be followed is, that the portable barometer and 

 the barometer of comparison should be as nearly as pos- 

 sible in stations where the local circumstances are the 

 same. A great distance or interval is not always an ob- 

 stacle ; so that M. Raymond has remarked that observa- 

 tions made by him on the Pyrenean Mountains, when 

 compared with those which M. Bouvard continually 

 makes at the Imperial Observatory, present a course of 

 changes of considerable regularity, whereas the same 

 observations of M. Bouvard, compared with those which 

 M. Raymond made at Marii la Ville, indicate from one 

 day to another, differences of ten or twelve metres or 

 yards in the relative height of the two stations : whence 

 it may be concluded, that the use of the barometer to 



measure 



