NO. 3 RADIATION OF THE ATMOSPHERE — ANGSTROM 1 35 



tion, readings of the psychrometer were taken by (Messrs. A. K. Angstrom 

 and E. H. Kennard, representing the Smithsonian Institution, during the 

 nights when they were observing. These readings have also been used to 

 check the meteorograph records. 



The exposure of the instruments was fairly good. They were kept in an 

 improvised shelter constructed from the boxes in which they were " packed " 

 to the summit. The ventilation was good, but during those afternoons in 

 which the sun shone, the air in the shelter was considerably heated. How- 

 ever, there were only four sunny afternoons, and furthermore, the eye readings 

 at 2 p. m. and 5 p. m. leave but little interpolation necessary. 



All of the instruments were calibrated before and after the expedition. 

 Especial care was taken in the calibration of the aneroid barometer, tests being 

 made to determine the correction for " lag " or " creeping " and for changes 

 in temperature. The effect of the latter was found to be negligible. 



Owing to the large scale value of the pressure elements in the meteorographs 

 and to the effect of changes of temperature on those elements, it is impossible 

 to obtain with much accuracy the hourly values. However, in table 5 are 

 given the pressures observed at certain hours. The readings at n a. m. are 

 uniformly higher than those at S a. m., 2 p. m., or 5 p. m. It is probable that 

 the diurnal maximum occurs at about this time. 



The range of pressure for the entire period is large, about 8 mm. The 

 range for the same period at Independence is much less, about 5 mm. At 

 both places the lowest readings were recorded on August 8 and 9, while a 

 cyclonic disturbance was central over northern California. This low was 

 attended by considerable cloudiness, with thunderstorms, and, at Mount 

 Whitney, snowstorms. The greater pressure range at Mount Whitney than 

 at Independence is accounted for by the cool weather during the passage of 

 the low and the consequent crowding together of the isobars in the lower 

 levels. 



Tables 6, 7, and 8 contain the hourly values of temperature, relative humidity, 

 and absolute humidity, respectively. Means have been computed for the 10 

 complete days, August 3 to 12, inclusive. Final conclusions may not be drawn 

 from so short a record, but a few comparisons are of interest. The mean 

 temperature was 0.7° C. ; that in the free air at the same altitude and for the 

 same time of year, as determined from five years' observations at Mount 

 Weather, Va., is — 2.0°. The mean temperature at Pikes Peak 1 for these 

 10 days in 1893 and 1894 was 2.8 . Pikes Peak has an altitude of 4,301 meters, 

 or about 100 meters below that of Mount Whitney, and to correct for this 

 difference in altitude about o.6° should be subtracted from the value at Pikes 

 Peak. The temperature at Mount Whitney was undoubtedly below normal, 

 owing to the severe stormy weather which prevailed. However, the values at 

 both places, compared with those at the same altitude above Mount Weather, 

 indicate that in summer temperatures on mountains are higher than those in 

 the free air, although difference in latitude, in this case about 2^°, should 

 be considered. The times of maximum and minimum temperatures at Mount 

 Whitney were 3 p. m. and 5 a. m., respectively; at Pikes Peak they were 

 1 p. m. and 5 a. m., respectively. 



1 Annual Reports of Chief U. S. Weather Bureau, 1893, 1894, 1895-1896, 

 Washington. 



