BAROMETRICAL AND METEOROLOGICAL OBSERVATIONS. 173 



aqueous vapor in the atmosphere upon its pressure, which we cannot bring into calcu- 

 lation in any other way with a reasonable hope of success. This constitutes one of 

 the most prominent advantages of the new method. Those formula?, in which the 

 atmospheric moisture appears as a separate element are open to a great many objec- 

 tions, and in then application we meet with obstacles which we are not now prepared 

 to overcome. The most prominent among them is our want of accurate knowledge of 

 the laws of the distribution and transmission of moisture through the atmosphere, and 

 the great variability of its amount in different strata of the air, depending partly on 

 altogether local influences, which may not extend beyond the lowest strata of the 

 atmosphere. Only under particularly favorable circumstances these formulae can be 

 expected exceptionally to give very favorable results. 



The new method required the use of a mean reading of the barometer and ther- 

 mometer at the fixed station, and the corrections which are applied give an approxima- 

 tion to the mean reading of the barometer at the station the altitude of which is to be 

 determined. If this mean was really obtained, then the mean temperature of the 

 place would give the correct result; but as the corrections fail to be perfect, the intro- 

 duction of the mean temperature of the respective day or days seems generally to 

 give the best results. 



CORRECTIONS FOR THE HORARY OSCILLATIONS OF THE MEK(TKLVL COLUMN. 



The horary oscillations differ according to the latitude, climate, and altitude of 

 the stations, and the seasons of the year. Their values for the regions traversed by 

 us were not known. I determined them, therefore, for as many points as it could be 

 done. Hourly observations were made for the purpose, mostly during 16 hours of 

 each day, and kept up for several days or weeks. From these the variations were 

 deduced, with the aid of diagrams and interpolations, as described by Lieutenant Ab- 

 bot. The following table exhibits the results obtained, which are also graphically 

 illustrated by the curves on Plate A, on an enlarged scale. The full black lines in those 

 diagrams connect the computed hourly means, while the dotted lines, like the values 

 put in brackets in the following table, are not actually determined by observations: 



A.— Correction* for tin: horary oscillation of the barometric pressure. 



