gg SMITHSONIAN' CONTIinU-TTONS TO KNOWLEDGE VOL. 27 



The wings as thus guyed were rigid enough, and in the field-trials of No. 5 



on May 8 and dime 6, did not yield noticeably under pressure, and there seemed 

 to be no serious default in their lifting power, but the guy-sticks were heavy 

 and the system was not again employed. The wings used in these trials, shown 

 in Fig. C, Plate Hi, had a frame of hickory, consisting of a front rib and nine cross- 

 ribs, over which the silk was tightly stretched. The curvature of the wings, 

 which is shown in the cross-sectional drawing, had a rise of about one-twelfth 

 the width, the highest point of curvature occurring about one-fourth the dis- 

 tance from front to rear. Each wing was 64 cm. x 192 cm. (25.25 in. x 75.75 in.), 

 the two with the tail, in surface equal to a single wing, having an area of 3.7 

 square metres (40 sq. ft.). The combined weight of the wings was 1150 grammes 

 (2.53 pounds), and of the tail, 583 grammes (1.28 pounds). 



The evolution of a vertical rudder had meanwhile been going steadily for- 

 ward. Those first used had been small, rectangular, stiff, aud heavy, but in the 

 experiments of May 8 a much lighter and larger construction, consisting of a 

 frame 92 cm.x76 cm. (36 in.x30 in.) covered with paper, was used, and on June 

 7 this was replaced by a long, diamond-shaped rudder, having a spruce frame 

 covered with silk, very light and seemingly more effective than any hitherto 

 used. 



I had in the meantime designed a " tail-rudder," consisting of a horizontal 

 tail and vertical rudder combined, each having an area of about 0.6 square 

 metres (6.5 sq. ft.) which, however, was not used until 1896. 



In August was begun the construction of a deeply curved and arched pair 

 of wings for No. 4, which consisted of a light framing of spruce elaborately 

 guyed and covered with gold-beater's skin drawn tight as a drum-head with 

 pyroxelene varnish. In their construction a new feature, foreshadowed in the 

 method of guying the separate wings used in the field-trials of May and June, 

 was introduced, which was adopted in all subsequent constructions — the guy- 

 stick, previously described as stretching lengthwise across the wing being now 

 made a part of the wing itself, which was thus provided with two longitudinal 

 ribs instead of one. The additional rib occupied a central position, and like 

 the front rib was attached to the midrod by means of a strong wing clamp. 

 Its outer end was united to the front rib, which was here bent into a quadrant 

 of a circle. This pair of wings had an expanse of 435 cm. (14.3 feet), an area 

 of 2.5 square metres (26.8 sq. ft.), a weight of 660 grammes (1.45 pounds), and 

 a depth of curvature equal to one-tenth their width. 



This construction offered a two-fold advantage in its resistance to both tor- 

 sion and bagging, for as the pressures upon the wing were nearly balanced 

 aboul the middle rib, the tendency to twist was reduced to a minimum, while 

 the bagging, which results from the bending of the framework, as distinct from 



