February 2i, 1890. J 



SCIENCE. 



are of the same sign, with reference to the annual mean, as the 

 temperature phases at such stations. This phase of barometric 

 pressure, which is the reverse of that in the parts of the United 

 States of low elevation, results from the lower average tempera- 

 ture of the winter months contracting the great body of air, 

 so that much of it is brought below the summit of the moun- 

 tain, while in summer reverse conditions obtain. 



The mean temperature of Pike's Peak is 19.3°, with a range 

 in the annual mean temperature of 4°, dependent on the 

 mean of 17.9^ for 1880 and 31.9° for 1879. The highest tem- 

 perature observed was 64°, July 19, 1879; and the lowest, 

 — 39", Dec. 21, 1887. As might be expected, the range at 

 Mount "Washington is considerably greater. The mean tem- 

 perature at this latter station is 26.1°, with a range in the 

 annual mean temperature of 4.5'^, — from 23. .5° for 1875, to 

 28° for 1878. On Mount Washington the highest temperature 

 recorded was 74*^, Aug. 9, 1873; and the lowest, — 50°, Jan. 

 23, 1885. 



The daily range of temperature on the summit of Pike's 

 Peak, as determined from ten years' observations with self- 

 registering instruments, shows that the maximum range occurs 

 in July and September (14.3° and 14.3° respectively), with the 

 minimum of 11.6" in December. The greatest range likewise 

 occurs at adjacent stations on lower level in the summer or 

 early fall, as shown by ten years' record at Denver, Col., with 

 - the greatest ranges (27.9°) in September and (27.3°) in July; 

 and at West Las Animas, Col., — record of five years, — (33.7°) 

 in October. At Denver the minimum range occurs in February 

 (33.5°), and at West Las Animas in May (29.5°). 



It thus appears that the mean daily range on the summit of 

 Pike's Peak is only about one-half of that which obtains on 

 the low plateau country to the eastward. The mean daily 

 range at Mount Washington differs materially from that of 

 Pike's Peak, it having its maximmii (18°) in January, whence 

 it decreases quite regularly to July (10.6°), and then rises 

 gradually to the winter maximum. The mean range — from 

 ten years' observations — on Mount Washinghton is 13.8°, 

 being only slightly less than that at Portland, Me. (15.4°), 

 and at Burlington, Vt. (16.5°). 



The precipitation of Pike's Peak exhibits peculiarities in its 

 distribution throughout the year, the amount rising from a 

 primary minimum in February to a secondary maximum in 

 April. A very decided secondary minimum occurs in June, 

 followed immediately in July by the primary maximum. The 

 amount of precipitation in the summer (35 per cent) is sub- 

 stantially the same as that in the spring (33 per cent) , the 

 remainder being very equally distributed throughoui the au- 

 tumnal and winter months. The June minimum appears very 

 remarkable, but its authenticity seems assured in view of the 

 fact that at Colorado Springs, at the base of the mountain, 

 and at Denver, nearly 80 miles to the northward, similar rain- 

 fall conditions obtain. At Denver the May rainfall is 18 per 

 cent; the Jime rainfall, 9.5 per cent; July, 11; against 15, 

 12, and 24 per cent respectively at Colorado Springs, and 13, 

 6, and 15 per cent on Pike's Peak. 



The mean wind-velocity throughout the year is graphically 

 represented by a curve with one bend or inflection; the de- 

 crease in velocity being, as a rule, very gradual, from 36.6 

 miles in January, to 12.5 in July and 12.3 in August. The 

 curve of the mean wind-velocity is substantially opposite in its 

 phase to the curve of the mean temperature; that is to say, 

 the highest mean monthly velocity occurs with the lowest 

 mean monthly temperature, and the least mean velocity with 

 the highest mean temperature. It is interesting to note that 

 the same general rule holds true as bearing on the relations 

 between the mean hourly temperature of the day and the mean 

 wind-velocity. The average hourly velocity of the wind for 

 the entire period decreases gradually from a mean of 33.3 

 miles per hour between 2, 3, and 4a.m,, to 17.5 miles between 

 11 A.M. and 13 noon. It is also noted that the minimum hourly 

 wind-velocity for every month in the year occurs between 

 11 A.M. and 12 noon; but the distribution of the hours of maxi- 

 -mum mean wind-velocity is somewhat irregular throughout 



the dififerent months of the year, varying from between mid- 

 night and 1 A.M. to the hours of 4 and 5 a.m. Doubtless, were 

 means of hourly temperatures available, it would appear that 

 the highest temperature occurs quite regularly at noon, while 

 the lowest temperature occurs more irregularly between midnight 

 and sunrise. In July the maximum hourly velocity is 15.5 

 miles against a minimum of 9; but in January the range of 

 the mean hourly velocities is very materially reduced, the 

 range being from 38 from midnight to 1 a.m., to 35.4 from 

 11 A.M. to 13 noon. 



Unfortunately, the direction of the wind was not automat- 

 ically recorded, but the prevailing directions are obvious from 

 the observations made thrice each day. It appears from these 

 observations that 31 per cent of the wind comes from the 

 south-west, 30 per cent from the west, 31 from the north- 

 west, 10 from th3 north, 8 from the north-east, and 5 from 

 the south; while 3 per cent pertains in each case to the east, 

 south-east, and calms. The direction of the wind changes 

 but slightly through the different months of the year; the 

 records showing that the maximum per cent comes from the 

 south-west from March to October inclusive, but during the 

 winter months the direction changes slightly, and the winds 

 from the west prevail from November to February inclusive, 

 with the north-west winds and the south-west winds of slightly 

 less frequency by 1 or 3 per cent. 



On Mount Washington, however, from nine years' observa- 

 tions, 54 per cent of the wind comes from the north-west, 12 

 per cent from the west, and 8 per cent each from the south- 

 west and north. 



The observations for two years at Colorado Springs, at the 

 base of the mountain, show, as might be expected, very 

 different wind conditions. From the situation of this station, 

 it might be inferred that the winds would blow from the north 

 or north-west, or from the south and south-east, which is the 

 case; the order of frequency being as follows: north, 37 per 

 cent; south-east, 33 per cent; north-west, 15 per cent; south, 

 10 per cent. The influence of topographical features upon the 

 wind is also clearly shown by the direction at Denver, where 

 38 per cent of the wind comes from the south, and 14 per 

 cent from the north. 



Severe and prolonged wind-storms are unusual on Pike's 

 Peak, and the days are comparatively infrequent when the 

 mean hourly velocity equals or exceeds fifty miles per hour. 

 The most remarkable wind -storms were those of Sept. 38-29, 

 1878, when the mean velocity for twenty-four hours was 71 

 miles, and Dec. 35, 1883, when the mean velocity was 70 

 miles per hour. The highest extreme velocity recorded at 

 Pike's Peak was comparatively low, being 113 miles. May 11, 

 1881. 



Velocities exceeding these have been frequently noticed at 

 exposed points on the Pacific and Atlantic coasts. Mount 

 Washington not only has higher winds than the summit of 

 Pike's Peak for short periods, but also for days or months. 

 On Feb. 37, 1886, the mean hourly velocity on the summit of 

 Mount Washington was 111 miles for the entire day, and in 

 January, 1878, the extraordinary velocity of 186 miles per hour 

 was recorded. The maximum monthly movement at Pike's 

 Peak was 38,691, in January, 1887; at Mount Washington, 

 36,515 miles for January, 1885, a mean hourly velocity 

 throughout the month of 49 miles, followed closely by a mean 

 of 48 miles for February, 1883. 



The mean annual cloudiness on Pike's Peak is 40 per cent, 

 ranging from 33 per cent in November, to 74 per cent in July. 

 The tendency is to an excess of cloudiness during the late 

 spring and the late summer, with the least amounts from 

 September to January inclusive. On Mount Washington the 

 cloudiness is much greater, averaging 57 per cent for the year. 

 The range at this latter station is also higher, varying from 

 53 per cent in September, to 61 per cent in March. The dis- 

 tribution throughout the year on Mount Washington appears to 

 be accidental, with possibly a slight tendency to less cloudiness 

 during the months of high temperature. 



Pike's Peak is celebrated for its electrical storms. Many 



