356 French National Institute. 



tiie sailie thing, in regard to the distance of the centre of 

 gravity from the po:;it of suspension, this consideration 

 alone conducts to a theorem analogous to the first of the 

 two, for which we are indebted to Huvgcns ; — a new proof 

 of the great iccundity of algebraical expressions, when one 

 has the art of giving the most proper forn> to all their de- 

 velopments. 



Measuring of Heights l<y means of ike Barometer. 



The celebrated experiment devised bv Pascal, and \Vhich 

 proved that a column of mercury decreased in proportion 

 as the barometer was carried to a greater height, after hav- 

 ing proved the gravity of the air, must have made the mer- 

 cury be considered as a scale capable of measuring the height 

 to which it is carried. But this scale being very small in 

 comparison of the heights which it ought to measure, it 

 was sopn perceived that it would be nccessarv to improve 

 the construction of the barometer so far as to render sensi- 

 ble and appreciable the smallest changes in the height of 

 the mercniv. The necessity of avoiding or of calculating 

 the continual variations which the barometer experiences, 

 even without changing its place, presented another obstacle 

 jnuch more torni'dable, and which seemed to take away all 

 hope j)f approaching the truth, or coming near it. These 

 difficulties, however, philosophers have been able to sur- 

 mount ; so that barometric measures, properly employed, 

 may vie in exactness with the trigononseirical measures, to 

 which they are superior on account of their facility and the 

 generality of the method. 



Among the difi'erent formulae given for the solution of 

 this problem, that of M. Laplace is distinguished by the 

 manner in which it has been deduced froni the(My ; but the 

 principal co-eilicicnt, drav.n from an observation which 

 appears not to have been free from error, might have need 

 of some moditication. This M. Ramond has examined in 

 a memoir, of which we shall give some account. By his 

 numerous experiments made on diflerent mountains, he 

 found what are the circumstances most favourable to such 

 observations, as well as the hours which ought to be chosen 

 or avoided ; for there are some causes tiic effects of which 

 must be very sensible, and ;vhich, however, it is impossible 

 always to take into account in calculations. Such are the 

 ascending or dcscea^ing v.inds,which, according to M. Ra- 

 mond, prevail -almost constantly at ceriain hours. Some, 

 by les^i:-nlng th*e' 'weight of the column of air with which 

 the mercury is \n equilibrium, must also lessen that column, 



and 



