CEOLOGtCAt OBSERVATIONS IN FRANCE. 211 



in Succession, and in which I shall point out generally the 



n^iire of the' countries mentioned, that ray labour^ may be 



more immediately useful to geoloj^y. 



All the heisi:hts were calculated according to the formulae Hcic^hts calcu- 



o? Messrs. de Luc and Trembley: not that I mean to speak l<ited according 



•^ . ' . to de Luc and 



of them as the only ones (it for practice ; I know there is a Trembley. 



method founded on different principles^ which was proposed 

 some years ago by a learned philosopher, and has a just 

 claim to oiir best attention : but my labours were in great 

 measure completed, before I was acquainted with it, so 

 that it would have been too laborious a task, to begin them 

 anew. 



They who have at heart the improvement of measuring Modes of as-- 

 heights by the barometer however would do well, to calcu- hdtrhts by the 

 late their observatioiis according to different formultE, for on barometer 

 this point the result of experience is chiefly to be considered, p^red wkh°tri- 

 and we have not yet a sufficient number of decisive facts, to gonometrical 

 induce us to employ one formula or method exclusively of '^^'^^ ations; 

 every other. It is desirable that some philosopher, residing 

 in the neighbourhood of a solitary mountain, should mea- 

 sure it trigonometrically with great exactness, and afterward 

 r-epeatedly ascertain its height by the barometer, calculating 

 his observations according to several formulae, and com par-* 

 ing their results with his geoinetrical n;ieasurement. It is and tried at ya- 

 particularly important, that these observations should be "*^"s seasoiis 

 made at all seasons of the year, and at different times of the ti^es brth^ 

 cliiy, so as to take in every variation of temperature: but in ^^y. 

 reality when mountains of moderate height are visited, we 

 ■generally find on them the same degree of temperature, and 

 most frequently that at which the various formulae give near- 

 ly the same results. We ought not to suppose therefore, 

 that the science has already attained such a degree of per- 

 fection, as to enable us to dispense with farther trials: the 

 only course to be followed appears to me to be that of tz^pe- 

 rience. 



The nec€ft!»ity of employiiSg good instruments is too ob- 

 vious to mention. It is likewise to be wished that th.e tra- When calculi*. 



veller, into whose views it may not ciiler to give heights with ^^^"'' ^""^ m^dc 



, ,..,„'? jn a loose way, 



any great precision, as the geologist m general. for instance, this should be 



V. on Id appiise us of this. It would farther be of advantage, mentioned. 



P 2 ' when 



