366 M. Delcros' Barometrical Measurement [Nov. 



atures are nearly the same, which we may ascertain for our 

 greater satisfaction. 



A similar undertaking remains to be executed for the formula 

 for barometrical measurement. This last is affected likewise by 

 horary influences. All the observers, and particularly M. Ra- 

 mond in his celebrated and useful researches, have pointed out 

 this effect. It is the coefficient for noon which has been gene- 

 rally adopted and applied to all the hours of the day ; for noon 

 would limit the barometrical method too much. We must 

 employ the whole day if we wish to obtain series of points, 

 profiles, &c. Let me then request zealous observers employed 

 in eievated situations, geodesically connected, to collect the 

 data requisite for the solution of this interesting problem. I am 

 at this moment employed in calculating a series of 112 corre- 

 sponding observations made with great care at two points, the 

 difference of whose heights has been trigonometrically deter- 

 mined. These observations were made at intervals of two hours, 

 from eight o'clock in the morning till six in the evening. If I 

 succeed in discovering any pretty constant law, I shall commu- 

 nicate it to the public. But it ought not to be concealed that 

 the determination of such laws ought to be the result of an 

 immense number of observations collected in all seasons, made 

 in all hours, and varied in many different places, and with 

 different horizontal and vertical distances. 



Paris, Feb. 15, 1818. DELCROS. 



Appendix by the Editors of the Bibliotheque Universelle. 



It may be worth while to quote, in support of our correspond- 

 ent's ideas, the opinion of a celebrated philosopher on the 

 comparison of the measurements of heights by the two methods 

 of trigonometry and the barometer. This opinion is found in 

 the memoirs of M.le B. Ramond " Surle Nivellement Barome- 

 trique des Monts Dores et des Monts Domes," presented to the 

 Academy of Sciences in 1815, in which he announces having 

 determined the absolute height of about 400 remarkable points 

 in the most interesting part of the department of the Puy-de- 

 Dome, and indeed of the whole of France. For this region, 

 which correspond^- to the mean parallel of our hemisphere, is 

 likewise the portion of the realm where the mountains are most 

 elevated, and the levels the most different and best characterized, 

 by the very different nature of the beds, mostly volcanic, but 

 belonging to epochs separated by veiy long intervals of time. 

 He has examined how the inhabitants, spontaneous vegetation, 

 and culture, are distributed on a vertical scale of 1900 metres, 

 between the 45th and 46th degrees of latitude. Called as he has 

 been more than once in the series of his operations to compare 

 his barometrical data with the geodesical results obtained by 



