BAROMETRICAL MEASUREMENT OF HEIGHTS. 



419 



TABLE X. 



correction for the hour of the day. 

 Argument, the Hour, and the Approximate Height in toises. 



Table XI. is found in the Resume des Observations Thermoinetrique ef Barome- 

 triques fait.es a Genere cl au Grand St. Bernard pendant Jes dix annees 1841 a 1850, 

 a very elaborate paper by Professor E. Plantainour, Director of the Observatory at 

 Geneva, published in Vol. XIII. of the Memoires de la Sociefe de Physique de Geneve. 

 The author, after having determined the difference of elevation between Geneva 

 (407.0 metres above the level of the sea) and the Great St. Bernard, by means of 

 the corresponding observations, made during these 10 years, and using his own tables 

 given above, reversed the problem. Assuming the difference of level thus found, 

 viz. 2066 metres, to be the true height of the layer of air between the two stations, 

 and its weight being given by the barometrical observations, he deduced from these 

 data its mean density, and from the density its mean temperature at every even 

 hour in every month of the year. Comparing these mean temperatures with those 

 given at the same hours by the half-sum of the temperatures taken at the upper and 

 the lower station, he found tiie differences contained in Table XI., which are the cor- 

 rections to be applied to the half-sums of the temperatures to obtain, in this particular 

 case, the true mean temperatures. The second part of the table has been computed 

 by multiplying each temperature in the first by 7.5 metres, in order to show the value 

 of that correction in barometrical measurements. 



D 79 



