1823.] Appendix to M. Ramond^s tmtrudiom, Sfc, ^55 



Article VIL 



An Appendix to the Abstract of M. Ramond's Instructions for 

 Barometrical Measurements, By Baden Powell, MA. of Oriel 

 College, Oxford. 



{Concluded Jrom p. 274.) 



In order to render more complete the foregoing compendium, 

 and as some readers may wish for an account of the principles 

 on which the formula is constructed, it may not be improper 

 here to add for their convenience a brief explanation of it, toge- 

 ther with some remarks on other points connected with the 

 subject. 



I. Outlineof the Demonstration of the Formula, 



M. Biot, in the small tract prefixed to his " Tables Barome- 

 triques Portatives," has given at large the demonstration of a 

 formula which differs from the present only in some very slight 

 modifications. I shall, therefore, do no more than present a 

 sketch of his elegant investigation, the principles of which may, 

 perhaps, be made sufficiently intelligible, without following him 

 through all the detail of his analytical processes. The reader 

 who is desirous of fully appreciating their beauty is referred to 

 the original. 



As 1 here propose only to give a mere outline of the investiga- 

 tion of the formula, it will be superfluous to go through the 

 elementary proof of the general theorem, which estabHshes the 

 relation between pressure and elevation. We may set out by 



assuming that the difference of elevation, % = ~ log. (^j 



M being the modulus of the common system of logarithms, and 

 C a coefficient involving the various corrections. 



(1.) Our object is to discover the coefficient C. This M. Biot 

 proceeds to do in the following manner : "^ — If we represent by S 

 the density of the air under the pressure h, that of mercury being 



s 

 unity, we have 3^ = C h, and - = C. We may obtain, there- 

 fore, the value of C, if we have, by very exact experiments, the 

 ratio of the densities of air and mercury, under a given pressure 

 of the atmosphere. 



This ratio is not the same in all countries ; for in all countries 

 the weight of bodies has not the same intensity, as we learn 



from experiments on the pendulum, and the ratio - varies with 

 the intensity of gravity. Indeed J^is the density of the air under 



• Mesures Barometriques, p. 7. 



2a2 



