ROTCU. — EXPLORATION OF UPPER AIR. 247 



The details of the work, as now carried on at Blue Hill, are as fol- 

 lows. The kites, which have no tails, are of Eddy's Malay, or of liar- 

 grave's cellular ty[)cs, the former presenting a convex surface to the wind, 

 and the latter two {)air of superposed planes, each pair being connected 

 by side planes. In addition to the two leading kites, others are attached by 

 independent cords to various points of the line, which is a steel music wire, 

 0.033 inch in diameter, having a tensile strength of three hundred pounds, 

 and weighing fifteen pounds per mile. The meteorogniphs are composed 

 mostly of aluminium and weigh less than three pounds each, the one con- 

 structed by J, Richard, of Paris, recording on a single clock cylinder atmos- 

 pheric pressure, air temperature, and relative humidity, while that made 

 by Mr. Fergusson similarly records wind velocity and air temperature. 

 One of these instruments is hung to the wire between two kites, in order to 

 insure its safety in case of breakage of the wire or of one kite, or the fail- 

 ure of the wind to support the latter. The wire is coiled upon the drum 

 of a windlass, which may be turned by two men, and a measuring device 

 registers the amount of wire uncoiled, while the angular elevation of the 

 meteorograph, when not hidden by clouds, is observed from time to time 

 with a surveyor's transit at the windlass or at the ends of a base line. 

 From these data, or from the barometric record, the altitude of the 

 meteorograph is calculated. Kites may be flown in all kinds of weather, 

 whenever the wind's velocity is between fourteen and thirty-five miles an 

 hour ; and since on Blue Hill the average velocity is more than eighteen 

 miles an hour, days are frequent when flights are jDOSsible. 



Probably the greatest elevation yet attained by kites, and certainly the 

 highest level to which kites have lifted a meteorograph, is 8,740 feet above 

 Blue Hill. This was accomplished, October 8, 1896, by the aid of nine 

 kites, having a total area of 170 square feet, which gave a maximum pull 

 at the ground of about 100 pounds.* The meteorograph remained during 

 several hours higher than a mile, and good records of the indications of 

 the barometer, thermometer, and hygrometer were brought down. More 

 than one hundred records of atmospheric pressure, temperature, and rela- 

 tive humidity of the air, or wind velocity, at intermediate heights up to 

 the extreme altitude just stated, have been obtained, and they are being 

 discussed for publication with the Blue Hill observations for 1896, in the 

 " Annals of the Astronomical Observatory of Harvard College." A few 

 general conclusions may be mentioned. At the height of about a mile the 

 diurnal changes of temperature in the free air nearly disappear, although 



* Science, Nov. 13, 1896, p. 718. 



