630 



Lieutenant Eennt on the Constants of 



years inclusive (for such observations vide M. Plantamotte's quarto, entitled 

 " Resume," &c.,&c., pages 8, 21, 29, and 37 ; also pages 51 and 57). 



The true height of the Convent above the Observatory, according to 

 extremely accurate spirit-levelling, is 2070'34 metres. — ( Vide tract, entitled 

 "Nivellement du Grand-Saint-Bernard," page 10, line 13 from the top of the 



Table I. 



True Height of Convent above the Oliservatory = 2070-34 metres. 



I have now to state, that the slight differences between the heights, as cal- 

 culated by the formulte of Plantamour, of Bessel, and of Eennt, as shown in 

 the above small Table, arise from the circumstance that these three formula3 

 do not employ the same value of the elastic force (or tension) of vapour of 

 water, — for with the same data of calculation these three formula give the 

 same results, — and seeing that the formula of M. Plantamour is only a slight 

 variation of that of Bessel, having a different value of the elastic force of vapour 

 of water, I shall not take the trouble of bringing it forward again, or applying 

 it to any other observations which may be hereafter noticed in this paper. 

 I have now to direct attention to the application of the four formula3 given 

 above to the calculated height of Mont Blanc above the Convent of the Great 

 Saint Bernard, obtained from observations, hygrometric as well as barometric, 

 made by Messrs. Bravais and Martins during their ascent of Mont Blanc, 

 29th August, 1844, compared with observations made at the Convent. — (For the 

 observations made by Messrs. Bravais and Martins, vide quarto, entitled 

 " Resume," &c., &c., page 70.) 



The height of Mont Blanc above the Convent has not been ascertained 

 either by spirit-levelling, or by the less accurate method of geodetic operations. 



