HIGHEST METEOROLOGICAL STATION IN THE WORLD. 255 



air temperature at Arequipa are very uuiforni tlirouglioiit the year. 

 The highest barometer reading was 22-(!7G inches on August 17, and 

 the lowest, 22-472, on January 11). The maximum thermometer read- 

 ing, which was exceptionally high, was 79° on June 3, and the lowest, 

 38-o°, occurred eight days afterwards. Although the teini)erature 

 nevxr descended to freezing, yet there are occasional frosts, and in the 

 clear season the intense radiation causes thin ice to form. The clear 

 season begins about the 1st ofAi)ri] and continues with scarcely an 

 Hiterrui>tion until the 1st of November. During -lanuary and Febru- 

 ary, 1892, most of the rain fell, amounting to 2 or 3 inches. In Febru- 

 ary, 1893, 1 inches fell in a single storm, but this appeared unprece- 

 dented and did great damage. The mornings are generally bright 

 throughout the year, most of the rain falling in the afternoon or even- 

 ing. Excepting during the rainy season, the air is exceedingly dry, 

 relative humidities of 3a per cent having been recorded in March, 1893. 

 The wind, as at low elevations, reaches its highest velocity in the mid- 

 dle of the day, and it is generally calm at night. For the year above 

 quoted, the highest velocity, 17 miles per hour, occurred in December. 

 Soon after sunrise a strong wind blows down from the mountains to 

 the northeast, after which the wind shifts, decreases in velocity, aud 

 resumes its normal course. 



The diurnal i)eriods of the atmospheric pressure and the air temper- 

 ature are interesting on account of the small amplitude of both, and 

 tlie phases of the former. Taknig the barograph records for December 

 at Mollendo at sea level, at Areipiijia (8.050 feet), and at the camp on 

 Charchani (1<»,G.")0 feet), the respective diurnal amplitudes are 0-1 inch, 

 0-07 inch, and 0-03 inch. Whereas, at the sea-level station, the chief 

 minimum and maxinnim occur about 5 P. M. and 11 r. m., res])ectively, 

 with secondaries at 4 A. m. and 9 A. M. ; at Arequipa, the chief mini- 

 mum occurs about 5 a. m., and the secondary minimum about 4 p. m. 

 Tlie night maximum, which is also the chief one, occurs at about the 

 same hour at both stations; but at Arequipa the secondary day maxi- 

 nnim is advanced to about 1 p. m. 



Not enough records at the Charchani station have been reduced to 

 determine definitely the pressure period, but there appears to be a 

 double daily maximum and minimum, Avhose times correspond in gen- 

 eral to those at Are(piipa. The noon and night maxima have nearly 

 equal intensities, but the morning minimum is deeper than the afternoon 

 one as at Areijuipa. These facts are the more interesting because some 

 preliminary observations by M. Vallot, on the summit of Mont Tjlanc 

 (altitude 15,780 feet), showed but a single maximum at about 1 p. m., 

 and a single miiiinmm about 4 A. m., with only a tendency toward a 

 secondary minimum late in the afternoon. At Cliamounix, in the val- 

 ley, the diurnal i)eriod is nearly the same as at Arequipa, so that the 

 form of the curve at the Charchani station may be partly due to the 



