230 USE OF KITES IN METEOROLOGICAL OBSERVATIONS. 



10.4(1 a. 111., uttiiined its greatest height at 4.15 p. m., and returned to 

 the ground at 8.40 p. iii. , its automatic recoixl ))eing shown in tig. 5, 

 in which the heights are expressed in meters and the wind velocities in 

 meters per second. The cumulus clouds were traversed three-quarters 

 of a mile from the earth, and aljove them the air was found to be very 

 dry. On the hill the air temperature was 72*^, when it was SS^ in the 

 free air 11,440 feet above, and the wind velocity increased from 22 to 

 40 miles an hour as can be computed from the scale of miles on the 

 right-hand margin of the anemometer record. 



During the past six j^cars, about two hundred and forty records have 

 been obtained at Blue Hill in all kinds of w^eather conditions, from the 

 ground up to 15,000 feet above it. They are published and discussed in 

 the Annals of the Astronomical Observatory of Harvard College, Vol. 

 xlii. Part I, and in several Bulletins of the Blue Hill Observatory, and 

 constitute, no doubt, the most thorough study of the lower air yet 

 made at a single station. The vertical distribution of temperature 

 and hmnidity has been investigated and six types have been deduced. 

 Normally, in tine weather, with increase of height the temperature 

 decreases at the adial)atic rate for unsaturated air (1° F. for 1S3 feet) 

 up to a certain height where there is a sudden rise of temperature, and 

 above that height the decrease is slower. This rise, which is caused 

 by a warm current overflowing a colder one, is noted by aeronauts also 

 at greater heights. Owing to the chilling of the air near the ground 

 at night it frequently happens that it is warmer at the height of a 

 thousand feet than it is at the ground, and as the relative humidity aloft 

 is generally the reverse of what it is at the groiuid, it follows that at 

 certain heights in the free atmosphere the nights are warm and dry 

 while the days are cold and damp. Contrary to the observations on 

 mountains, the diurnal period of temperature usually disappears above 

 a mile, but the changes due to cold and warm waves occur simultane- 

 ously at the ground and at the extreme heights reached by the kites. 

 The observations obtained during the passage of cyclones and anti- 

 cyclones indicate that the cause of the cyclone, at least in our latitude, 

 is its higher temperature with respect to the surrounding air. This 

 conclusion agrees with the convectional thcor}" of Espy and Ferrel, l)ut 

 it is possible that the shallow cyclones felt at the earth's surface may 

 have superposed on them other cyclones with cold centers. 



Atmospheric electricity is noticeable since the use of wire as a flying 

 line whenever the kites rise higher than a quarter of a mile above the 

 ground. Usually the wire becomes strongly charged with electricity 

 when great heights are reached and this is discharged in bright sparks 

 at the reel. The potential generally increases with altitude, and prob- 

 ably the electricit}^ is sometimes positive and sometimes negative, 

 although" no measurements have been made with the kites very high. 



