[Illustration: FIG. 18. MILITARY TRACTOR NO. 50 AT 3,500 FEET ALTITUDE _Photographed October 20, 1915_ The airplane, in which the pilot, Oscar Brindley and the observer, Meteorologist Carpenter, made their flight, was photographed at the maximum elevation, 3,500 feet above the aviation field.] [Illustration: FIG. 19. FLYING SQUAD’S WIND-DIRECTION PENNANT ON TOWER _Photographed October 5, 1915_ The regular observation tower from which all observations and notes on every flight are made is just back of the headquarters building. The station anemometer is on the tower, and the portable anemometer is to the left.] [Illustration: FIG. 20. THE AVIATION SCHOOL MOTOR-BOAT “PRONTO” _Photographed October, 1915_ During the flying periods, the motor-boat of the U. S. Aviation School is kept ready for instant service in order to work in conjunction, if needs be, with the Medical Corps emergency truck on land. Such is the speed of this boat (exceeding 40 miles per hour) that the water no longer has resiliency, and it is about as comfortable as riding in an old-fashioned stone-boat over rocky pastures.] [Illustration: FIG. 21. U. S. AVIATION FIELD AT THREE THOUSAND FEET ALTITUDE _Photographed October, 1915_ Part of Coronado and the portion of land called North Island, separated by Spanish Bight. Point Loma may be seen at the extreme upper right-hand corner of the photograph. The flying-machine sheds, buildings of the Aviation School, etc., may be seen in the immediate foreground. The U. S. Cavalry camp is the white splotch in the center foreground.] [Illustration: FIG. 22. REPAIR SHOP U. S. AVIATION SCHOOL, SAN DIEGO, CAL. _Photographed October, 1915_ In the repair shop of the U. S. Aviation School at North Island the motors are given a gruelling test, being run twenty-four consecutive hours at a speed greater than that given them in actual practice. After this run they are taken down and each part is spread out on a large drawing-table and is subjected to close scrutiny so as to show any defect. Several airplanes as well as seaplanes have been reconstructed in this shop.] * * * * * * Transcriber’s note: Punctuation and spelling were made consistent when a predominant preference was found in this book; otherwise they were not changed. Simple typographical errors were corrected. Ambiguous hyphens at the ends of lines were retained; occurrences of inconsistent hyphenation have not been changed.