the Barometric Formulce, ^-c. 627 



my observations, hygrometric and barometric, made near to Montreux, some 

 time before I had heard of M. Plantamour or liis labours in this depart- 

 ment of science, making use of my own formula before I had seen or heard 

 anything of Bessel's formula. It is satisfactory to reflect that, as to results 

 of calculation, there is a perfect agreement between those of Bessel's for- 

 mula and those of my own, although their forms are strikingly different. 

 The truth of this statement will appear by-and-by, when we apply them to a 

 series of observations, hj'grometric and barometric, made during a continuous 

 period of ten years, from 1841 to 1850, both years inclusive, by night as well as 

 by day, at the Convent of the Great Saint Bernard and Observatory of Geneva. 

 This accordance is equally striking when we apply the formulis to observations 

 made simultaneously at Mont Blanc and the Convent .of Great Saint Bernard, 

 and to my own observations made near Montreux in the spring of the year 

 1857. 



Before I present to the Academy such results, I desire to state clearly my 

 reason for believing that the constant recommended by Laplace, viz., 183360 

 metres, is altogether too small, and ought to be replaced without hesitation by 

 the new constant, 18404'9 metres. In the first place, the height which it gives for 

 Convent Saint Bernard above Geneva Observatory is less than the true height, 

 ascertained by accurate spirit-levelling, by more than 16'0 metres ; whereas, 

 the error by my new constant is little more than 4-0 metres being less than 

 error by Laplace's constant by 12-0 metres. True it is, that part of the error 

 of Laplace's formula is to be attributed to the fact that the allowance for the 

 presence of vapour of water, according to Laplace's unhappy mode of allowing 

 for it, is too small by more than 3 metres ; yet, taking this into account, there 

 remain 9 metres of error to be accounted for. There can be no doubt, there- 

 fore, that the constant is too small, and indeed this can be proved by the very 

 mode employed by Laplace in arriving at it. For if we consult the tract, 

 entitled " Sur la determination des Hauteurs par le Barometre par Monsieur E. 

 Plantamour" (being one of the two tracts presented by me to the Academy), 

 at page 6 we read that Laplace, in the calculation of his constant (viz., 

 1833G-0 metres), made use of a set of observations, barometric and thermome- 

 tric, by Ramond, in the Pyrenees, made at noon in the fine weather of the 

 summer months. 



