THE EXPLORATION OF THE FREE AIR. 321 



The method of making- a kite flight for meteorological purposes at 

 Blue Hill is as follows: Two large kites, fastened by their cords to the 

 ring in the main wire, being in the air the meteorograph is hung to the 

 ring by a cord with a spiral spring^ interposed to lessen shocks. The 

 kites are then allowed to rise and to unreel the wire until the angle with 

 the horizon becomes low, when, by means of the clamp just described, 

 another kite is added, and so on. After a pause at the highest attain- 

 able altitude the reel is connected with the steam engine and the kites 

 are drawn down. The pauses at the highest point, and when kites are 

 attached or detached, are necessary to allow the recording instruments 

 to acquire the conditions of the surrounding air, and because at these 

 times the meteorograph is nearly stationary, measurements of its angu- 

 lar elevations are then made with a surveyor's transit. Since the length 

 of the wire is known the height of the meteorograph can be calculated, 

 it having been found that the sag of the wire or its deviation, either in 

 a vertical or horizontal plane, from the assumed chord of the approxi- 

 mate arc which the wire follows, does not introduce an error of more 

 than 3 per cent in the height so computed. When the meteorograph is 

 hidden by clouds the altitude is computed from the barometer record 

 by Laplace's formula. The time of making each angular measurement 

 is noted in order that the corresponding point on the curve of the 

 meteorograph may be determined. 



The greatest heights ever reached by kites were above Blue Hill in 

 the autumn of 1897. On September 19, the meteorograph was lifted 

 9,250 feet above the hill which is 630 feet above sea level. Seven kites, 

 having a total lifting surface of 213 square feet, were employed to lift 

 it and the wire which weighed about 60 pounds, was nearly 4 miles in 

 length, and transmitted to the reel a maximum pull of 150 pounds. 

 The flight occupied less than six and a half hours, and during nearly 

 five hours the meteorograph was a mile or more above sea level. On 

 October 15, the meteorograph was raised still higher by only four kites, 

 of which the largest was Lamson's aero-curve kite, already described, 

 the total liftiug surface being 153 square feet. The height of 11,080 

 feet above the hill, or 11,710 feet above the sea, was reached with nearly 

 the same length of wire and amount of pull as on September 19. The 

 velocity of the wind at the ground varied from 13 to 22 miles per hour 

 during the flight, which occupied but four and a half hours. In both 

 these flights the temperature fell on the average about 1° F. for each 360 

 feet of ascent, but in the day the decrease was slower in the upper air, 

 confirming Glaisher's observations in balloons. Although the sky was 

 clear, strata of high humidity were encountered both in the ascent and 

 descent, corresponding to the levels at which the cumulus and alto- 

 cumulus clouds are known to form. At the highest altitude the air 

 contained a very small percentage of moisture. 



To understand the value of such data it may be necessary to state 

 that the progress of the science of meteorology demands a knowledge 

 of the conditions high above the earth's surface. Although some of 

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