78 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



degree of elasticity, which was at first provided in the frame of the rudder, but 

 was later given by a flat wooden spring, by which it was attached to the aero- 

 drome. The tail in this form now became the sole means of controlling the 

 equilibrium, and the results obtained with it were so very satisfactory that no 

 further attention was given either to the gyroscopic control built during the pre- 

 vious summer, or to any of the electrical forms of control constructed prior to 

 that time, all of which involved more or less delicate apparatus. 



The definite form into which these ideas crystallized is perhaps best exem- 

 plified in the letter of instructions issued by Mr. Langley on November 30, 18 ( J5 

 to the men employed on the work. The text of this letter is given in the Ap- 

 pendix, and the forms referred to in it for recording the weights and adjust- 

 ments of the aerodromes are those used in the data sheets after this time. 



In October work was resumed on Aerodrome No. 5, on which nothing had 

 been done since its test on June 7. The reconstruction of " Old No. 4 " into 

 " New No. 4 " which had occupied the entire summer, and the final result of 

 which was the production of a machine so radically weak as to be useless, had 

 been so discouraging that it seemed vain to attempt in any way to decrease 

 the weight of No. 5. The addition of the rear wings in place of the tail had, 

 however, so greatly increased the supporting surface that it seemed possible 

 that No. 5 might now be able to fly with no greater engine power than it had 

 on June 7. Some weak places in its frame were, therefore, strengthened and 

 the midrod at the front was raised five centimetres in order to raise the center 

 of pressure farther above the center of gravity and give the front wings a 

 greater range of adjustment. Some slight changes were also made in the gear- 

 ing which drove the pump, so as to make it work faster, and new burners, boilers 

 and a gasoline tank were constructed during November. Later the midrod, which 

 had formerly consisted of two separate pieces attached at the front and rear 

 respectively of the main frame, was made continuous, and in order to avoid 

 passing it through the smoke-stack, the stack was made to fork at this point. 

 These changes are clearly shown in Plates 14 and 15, which are photographs taken 

 on December 3. This plan was, however, soon changed so that the midrod 

 passed through the smoke-stack and was rigidly attached to the frame at several 

 points, and a new pump and new boilers were substituted for those which had 

 been worn out. Aside from these changes, which although small, added very ma- 

 terially to the general strength of the frame, no important changes were made 

 in No. 5 prior to its remarkable flight of May G, 1896. 



While these changes were being made in No. 5, similar ones were also being 

 carried out in New No. 4, and the addition of the rear wings to No. 4, together 

 willi other slight changes, made it such a distinctively different machine from 

 what it had been, that it was now designated as No. 6. After making extensive 



