the Barometric FormvlcB, S(C. 



631 



The importance of tlie following small Table, -which gives the results of the 

 application of the four formulaj to Mont Blanc and the Convent of Saint Bernard, 

 consists in its pointing out the harmony between the workings of Bessel's for- 

 mula and of my own. It also shows in a striking manner the peculiar defect 

 of the formula of Laplace, as also that by Bayley, in making allowance for 

 the hygrometric state of the atmosphere, when the mean temperature, as given 

 by the detached thermometers, is below the freezing-point, which was the case 

 during the ascent of Mont Blanc by Messrs. Beavais and Martins. 



The respective heights of Mont Blanc above the Convent of the Great Saint 

 Bernard, as obtained by the four formulsE, from observations by Bravais and 

 Martins, compared with observations made at the Convent, are as follow : — 



Table II. 



By this Table it appears that Laplace's formula diminishes height in mak- 

 ing allowance for influence of vapour of water of the atmosphere, whereas 

 the real operation of the action of vapour of water is of quite an opposite 

 character. 



I have now to bring before the Academy a subject of great importance, viz : 

 — The horary correction, without which the calculations for height, made by 

 help of the most correct formulas, from even an extremely great number of 

 observations, hygrometric as well as barometric, are subject to very serious 

 errors indeed. 



In the tract, entitled " Sur la Determination des Hauteurs," &c., M. Planta- 

 MOUR has given a small table of horary corrections for every second hour of the 

 four seasons (viz.. Winter, Spring, Summer, and Autumn). But inasmuch as 

 M. Plantamour knew not the correct height of the Convent Saint Bernard 

 above the Observatory of Geneva, as since ascertained by accurate spii-it-level- 

 jing, and seeing that M. Plantamour has calculated his small table of horary 

 corrections from incorrect data, this praiseworthy attempt of 1\I. Planta- 



VOL. xxiii. 4 



