18 Baron Cuvier's Historical Illoge of Baron Ramond. 



barometrical observations at the same points with the minutest 

 attention, showed how much the coefficient should be increased. 

 He determined with the same care the other numbers, and he 

 also paid attention to a number of momentary circumstances 

 which disturbed the accuracy of the observations, and the in- 

 fluence of which he learned to avoid. Among this number, 

 are the prevailing winds, the daily variations of the barometer, 

 the facility with which the thermometer, especially in moun- 

 tains, experiences from the earth, — an impression different from 

 that which the heat of the air would produce if acting alone. 

 The appreciation of all these effects required journeys, expe- 

 riments, and calculations without end ; and M. Ramond put 

 Jiimself to so much trouble about it, that a wit one day asked, 

 if the prefect intended to measure his conscripts by the baro- 

 meter. The truth is, that the barometer has become by his 

 means a geodetic instrument, which gives to geographers and 

 engineers, with great economy of time and labour, the heights 

 of high grounds and summits, too much neglected in ancient 

 chartSj and which even permits them to employ these heights 

 as bases for measuring horizontal distances. It is particularly 

 an instrument of the first importance to the geologist, whom 

 it enables to take the level of a formation wherever it appears, 

 and thus to assign its absolute position in spite of all the de- 

 positions by which it may be masked. 



M. Ramond has himself derived great help from the baro- 

 meter, in completing the history of the two most interesting 

 chains of Auvergne, the Monts-Dome and the Monts-Dores. * 

 The simple operation of levelhng had led him to discover be- 

 tween the lavas of different ages remarkable differences of struc- 

 ture. The most ancient appear to have preserved their fluidity 

 well for a long time, and to have been carried to much greater 

 distances from the mouths which discharged them. They com- 

 prehend not only the basalts properly so called, but porphy- 

 ries, petrosilex, clinkstones, which are not less than basalts the 

 products of an igneous fusion, and which often divide them- 

 selves, like the basalts, into columnar prisms. The more recent 



• "Nivellcraent baronietrique des Monts-Dores, et des Monts-Domes, dis- 

 pose par ordre des terrains," presented totlie Institute on the 24th and 31st 

 July 1813. 



