84?^ ON THE ELECTRIC COLCMNj 



the determined law of the densities of air correspondent ta 

 the dift'erences of pressure, in a given temperature of the 

 air. 2. An equation for the differences of actual tempera* 

 tures with that fixed point. By dint of trials, I arrived so 

 far in these determinations, that the method of measuring 

 tlie height of mountains by the barometer has been found 

 preferable to geometrical operations, on account of the im- 

 possibility of determining a law in the terrestrial refractions I 

 beside the difficulty of finding proper bases for the triangles. 

 But though the ineasurement of heights had been my first 

 view in this undertaking, other modifications of the atmos- 

 phere became soon predominant in my pursuit, as I shall 

 now explain. 



In order to ascertain the degree of exactness, which could 

 be obtained in the determination of the two parts of the 

 formula above defined, 1 had measured the heights of 14 

 points above one another on Mount ^a/et'e, near Geneva; 

 the whole height, above the level of the base that I had 

 chosen, being above 3000 feet; and at each of these deter- 

 mined elevations I had made a great number of ol>servation9 

 of the 6arojne/er in, different temperatures, both in the same 

 days and in different seasons. I had taken all possible pre- 

 cautions to ascertain the height of each of these points, in 

 verifying the trigonometrical operation by levelling the whole 

 mountain in passing by these points, in order that the 

 formula might be applicable to other places ; but had there 

 been some inaccuracy in that respect, it could not affect the 

 coefficients of the two laws, as applied to the same places ; 

 for if these laws had been sufficient, the formula would 

 have assigned to them the same height by every observation. 

 Anomalies ap. Now, no coefficient to the differences of heights in the 

 aTmosniier'ic"' barometer^ associated with any equation for the differences of 

 pheaomena. the thermometer, could bring the formula to express thie 

 same differences of height between the mm^ points: o. proof, 

 that the two conditions, ^ith which alone the formula cor- 

 responds, do not embrace all the causes of variation in the 

 density of air. Havings however no other data, \ fixed 

 these two parts of the formula in the mann«r the most cor- 

 respondent to the whole of my observations amounting to 

 ?iear GQ9 ; so that the sums gf anomalies in plus and minus 



comparatively 



