1865.] and Temperature in Barometric Hypsometry, fyc. 279 



may therefore be considered as the normal alteration of temperature. In 

 order to secure simultaneous observations at both stations for each section, 

 it would be necessary to have two ascending parties, one for each variable 

 station, each of which should be able to signal to the other. A stationary 

 observer at the lowest station would serve as a check on the other two. 

 This method introduces many practical difficulties, but the reduction of 

 the observations is rendered very easy by Tables I. and II. The great 

 importance of thus calculating heights by sections will be rendered evident 

 by the following examples. 



Taking the data in the Ann. Mettor. de F. for 1852, p. 70, we have for 

 Geneva as the lower and St. Bernard as the upper station, L 46, 

 B' 0-72643 A' 8-97 H t 408, 



V 0-56364 ' 1-89 Ji r 2463. 



Again, for St. Bernard as the lower and Mont Blanc as the upper station, 

 B' 0-56803 A' 7'6 H x 2463, 



V 0-42429 a! 9'1 A x 47877; 



which has been calculated as Ex. 2 above. 



But taking the data from the Annuaire du B. des L., 1865, p. 324, we 

 have for Geneva as the lower and Mont Blanc as the upper station, 

 B 729-65 M' 18-6 A' 19-3 H, 408, 

 6 424-05 ml 4'2 a 7'6 A, 4815-9. 



That is, the height of Mont Blanc above the sea, when calculated from 

 observations at Geneva, St. Bernard, and the summit, is determined as 

 4787" 7 metres, but when calculated from observations at Geneva and the 

 summit only, is determined as 4815-9 metres, or 28*2 metres more. This 

 is striking enough, but it is by no means clear that even the smaller amount 

 may not be too large*. 



station B' 30, AGO, H 0, L45, and supposing the temperature to decrease according to 

 Mr. G-laisher's Tables. The increase of height for each inch of depression was then 

 divided by the number of feet of ascent in which, according to Mr. Glaisher, the tem- 

 perature falls one degree at the height reached. 



* In the Ann. Met. de F. (1. c.) M. Plantamour calculates the height of St. Bernard 

 by Bessel's formula (taking account of the humidity of the atmosphere according to his 

 hypothesis, which is, however, not in accordance with Mr. Glaisher's observations) as 

 2473 metres. In the Annuaire de la Societe Meteorologique de France, 1853, p. 249, 

 M. Plantamour gives the height of the basin of the barometer at the hospice of 

 St. Bernard as 2493 metres, but does not there state how this result was obtained. 

 These heights being respectively 10 and 30 metres greater than that calculated by 

 Laplace's formula, would, if adopted as the height of the lower station in the second 

 calculation, give results more nearly in accordance with those in the third calculation. 

 The object here, however, is to examine the action of Laplace's formula only, and hence 

 the height assumed for St. Bernard must be that due to that formula. But different 

 data give different results for this height. Geneva and St. Bernard are too widely 

 separated horizontally, and have generally too great a difference of temperature, to 

 enable us to calculate the whole height in one section with any degree of confidence, as 

 there are probably many abnormal intermediate changes of temperature which, as will 

 be seen, tend to vitiate the result. Nor can any reliance be placed on adopting the 

 mean barometric pressures and temperatures. If any mean be taken, it mu^t be the 

 mean of many heights separately calculated from their individual data. 



