522 



SCIENCE. 



[N. S. Vol. XII. No. 301. 



wind exceeds 20 meters per second (true 

 velocity). 



When the kite flies at an altitude of 65° 

 its vertical height is about 90 per cent, of the 

 length of the flying line. Greater efficiency 

 is desirable, but at these steep altitudes the 

 kite is not always easily or safely managed 

 when near the ground, especially in variable 

 winds, or when the kite is being reeled in. 

 In the latter case any slight pull upon the 

 line brings the kite beyond the zenith, 

 where it becomes unstable and difficult to 

 handle safely. Refinements in construction 

 may probably remove this defect, but at 

 present it does not seem likely that any 

 great improvement in stability or efficiency 

 may be expected very soon. It is very de- 

 sirable to know what form of curve for the 

 lifting surfaces is most efficient, also if a 

 lighter, stronger and more easily built frame 

 may be developed. 



At present, kites strong enough to with- 

 stand winds of 20 to 30 meters per second 

 or higher require a velocity of 5 meters per 

 second or higher to lift them with the me- 

 teorograph ; and since the larger kites are 

 heavier per unit area than the smaller ones 

 it does not seem desirable to construct kites 

 having an area exceeding 9 square meters. 

 Moreover, such large kites are difficult to 

 handle in high winds. 



Steel music wire remains the best mate- 

 rial for line, although efforts have been made 

 without success to obtain material of greater 

 tensile strength. At the beginning of the 

 use of wire at Blue Hill, in 1896, it seemed 

 best to use a small wire, since the smaller 

 wires are slightly stronger, weight for 

 weight, than the larger; and with the ex- 

 ception of a short piece of ISTo. 11 wire pur- 

 chased for trial, No. 14 wire alone was 

 employed until February, 1900, when 7000 

 meters of ISTo. 17 wire were obtained. Tests 

 of the three sizes of wire showed that when 

 the smallest wire was employed, the limit 

 of safe working strain was reached before 



the angular altitude of the kites became as 

 high as that reached when the largest wire 

 was employed, although the larger wires 

 were appreciably heavier for the same 

 strength than the smaller. To determine, 

 if possible, the size of wire best adapted for 

 use, the tensile strengths and weights of all 

 sizes of music wire larger than No. 10 were 

 obtained from two leading manufacturers, 

 and are given in the accompanying table. 

 The data from the different sources did not 

 agree exactly and the figures in the table 

 are averages. 



DIAMETER, WEIGHT AND TENSILE STRENGTH 

 OF MUSIC WIRE USEFUL AS KITE LINE. 



A careful examination of all the data 

 shows that the cause of the greater effi- 

 ciency of the larger wires is that they pre- 

 sent relatively less surface to the wind than 

 do the smaller ; and that, instead of being 

 an insignificant eflect, as some have sup- 

 posed, the pressure of the wind upon the 

 wire is a most important one. The surface 

 of a No. 17 wire presented to the wind is 

 nearly one square meter for each thousand 

 meters of length ; and since, in very high 

 flights 8,000 to 12,000 meters of wire are in 



