USE OF KITES IN METEOEOLOGICAL OBSERVATIONS. 227 



steel wire which bind them in all directions. The average weight is 

 about 2 ounces a square foot of lifting surface, which is about the same 

 weight a square foot as the Eddy kites, when all the surface is included 

 in the estimate. The largest of the Hargrave kites stands 9 feet high, 

 weighs 11 pounds, and contains 90 square feet of lifting surface, which 

 in the recent kites is arched, resembling the curvature of a bird's wings 

 (tig. 2. PI. I). These curved surfaces increase the lift, or upward pull, 

 more than the drift, or motion to leeward, and so the angular eleva- 

 tion is augmented without materially adding to the total pull on the 

 wire, which should not exceed one-half its breaking strength. Another 

 efficient form that has been used at Blue Hill is the "aero-curve kite," 

 made by Mr. C. H. Lamson, of Portland, Me., and shown in tig. 3, 

 (PI. II). In flight it resembles a soaring bird, and when not in use 

 it can be taken apart and folded up. Mr. Lamson has recently con- 

 structed a similar kite, with three superposed surfaces, that has l)een 

 the leader in some of the highest ilights. 



A most important factor in the success of the Blue Hill work was 

 the application b}" Mr. Clayton, of the observatory, to every kite of an 

 elastic cord inserted in the lower part of the bridle to which the flying 

 line is attached; Avhen the wind pressure increases, this stretches and 

 causes the kite to diminish its angle of incidence to the wind until the 

 gust sul)sides. A kite can lie set to pull only a fixed amount in the 

 strongest wind, when the kite will fly nearl}^ horizontal. We are 

 therefore able to calculate the greatest pull that can be exerted on 

 the wire by all the kites, and with this device the kites have flown 

 through gales of 50 or 60 miles an hour without breaking loose or 

 injuring themselves. In general, the angle of the flying lines of the 

 Blue Hill kites is 50° or 60° above the horizon, and in winds of 20 

 miles an hour the pull on the line is about 1 pound for each square 

 foot of lifting surface in the kite. Kites can be raised in a wind that 

 Ijlows more than 12 miles an hour at the ground, and as the average 

 velocity of the wind for the year on Blue Hill is IS miles an hour, there 

 are few days when kites can not be flown. In order to fly in the 

 feeblest winds possible a small and« light pilot kite has been used to 

 help lift the large and heavier kite into the stronger and steadier wind 

 that usually prevails a short distance above the ground. 



The wire to which the kites are attached is steel nuisic wire, 0.032 

 inch in diameter, weighing 15 pounds a mile, and capable of with- 

 standing a pull of 3(»0 pounds. The wire is spliced in lengths of more 

 than a mile with the greatest care, special pains Ijcing taken that no 

 sharp bends or rust spots occur which would cause it to break. To 

 lift the increasing weight of wire, kites are attached at intervals of a 

 few thousand feet by screwing on the wire aluminum clanq^s to which 

 the kite lines are fastened, so that the angle may be maintained as 

 high as is consistent with a safe pull. Since each kite adds to the 



