Contrasted with the photograph of Point Loma on the opposite page, this picture shows the ideal water conditions for trying out seaplanes. Shortly before this picture was taken, one of the pilots of the Curtiss Aviation School, also on North Island drove a big seaplane 100 miles per hour barely skimming the surface of the water.] [Illustration: FIG. 12. INSTRUCTOR BRINDLEY AND METEOROLOGIST CARPENTER IN MILITARY TRACTOR NO. 50 _Photographed October 20, 1915_ Instructor Oscar Brindley and the observer, Meteorologist Ford A. Carpenter, U. S. Weather Bureau, leaving the ground for a flight. In the military tractor used generally by the Army, the observer sits forward while the pilot occupies the after cockpit. This machine, like all others used in the military service, has dual control.] [Illustration: FIG. 13. MILITARY TRACTOR NO. 50. TYPE OF BIPLANE USED IN U. S. ARMY SERVICE MADE BY GLENN MARTIN, LOS ANGELES, CAL. _Photographed October, 1915_ Motor, horsepower, 80: revolutions per minute, 1,277. Diameter of propeller, 8 feet. Load of 39 gallons gasoline, 2½ gallons oil. Flying radius with normal equipment, two persons, 300 miles. Maximum altitude obtained with this model at San Diego, 13,000 feet. Wing-spread, tip to tip, upper, 38 feet, 10 inches; lower, 34 feet, 10 inches. Supporting area, upper, 139 square feet; lower, 165 square feet; total, 364 square feet. Length of fuselage from rear of propeller hub, 21 feet, 6¾ inches. Data from Major F. P. Lahm, Signal Corps, U. S. A. Dated May 9, 1916.] [Illustration: FIG. 14. “TRIMMING” A TRACTOR IN LEAVING THE GROUND _Photographed October, 1915_ Military Tractor No. 50 just before leaving the ground. In gusty weather the mechanicians steady the ends of the lower planes, sometimes turning it by holding one edge and pushing the other. In the photograph the mechanicians are giving the airplane steerageway to the right.] [Illustration: FIG. 15. MILITARY TRACTOR NO. 50 JUST LEAVING THE GROUND _Photographed October, 1915_ Before attempting to leave the ground there is always considerable jockeying for a favorable head-wind, and the photograph shows Instructor Brindley maneuvering for a favorable pointing. After leaving the ground, the wind, so long as it is not gusty, makes no difference to the pilot.] [Illustration: FIG. 16. SAN DIEGO HARBOR AT OVER 2,000 FEET ALTITUDE _Photographed October, 1915_ The new municipal wharves are in the middle foreground and to their right may be seen the Santa Fé station. Part of North Island is obscured by cloud.] [Illustration: FIG. 17. THIRTY-FIVE HUNDRED FEET ABOVE SAN DIEGO _Photographed October, 1915_ This photograph was made 1,000 feet above the clouds. The wharves of San Diego and Coronado may be seen in the foreground and in the middle distance.]