Ease of Vision at 3,500 Feet Altitude.—At this altitude the ease of vision is most remarkable. At this height, with perpendicular vision, the eye is possessed of wonderful powers. In those “solitudes august with stars” men not only “mount up with wings as eagles” but are given the eagle’s unobstructed vision. Birds have been credited with much too keen vision. From this height of several thousand feet every object stood out with remarkable distinctness. Automobiles racing along the El Cajon boulevard to Lakeside were readily picked up with the unaided eye although 20 miles away. Looking down over the aviation field the long compass mark and the wind-direction pennant (Figs. [19] and [20]) were easily distinguished. The bay and ocean, however, gave the most remarkable revelation, for the bottom of the bay and the shallow ocean shore were plainly discernible. The absence of water as well as air refraction explains why submarines cannot hide from an airplane: one of the army aviators told me that a submarine cannot ordinarily sink so low that it cannot be seen from an airplane.
Color of Landing-ground Important.—Owing to the absorption and reflection of sunlight, there is a distinct variation in the character of otherwise similar landing-ground. A field, dark from recent plowing (or burning), will heat the air over it faster than will a field of stubble, hence over the former field there will be the greater air disturbance, and this will affect the ease of landing. Air is heated by contact and convection. One of the aviators said that recently he was descending, and had all but reached the ground when a localized convectional current hurled his machine upward some distance but immediately afterward deposited him on the ground without damage.
Spiraling Down 3,000 Feet.—Speeding ever in wide circles the course lay southeast over the upper part of San Diego Bay. The city of San Diego presented the usual checkerboard appearance ([Fig. 16]), and even at this altitude it would seem easy to drop an orange at almost any point. The velo cloud was lifting and we could see the gradual disappearance as it melted rather than drifted from North Island. (See [Fig. 17].)
The gliding descent was made from an altitude of 2,500 feet, starting above San Diego. As the aviation school was approached, we could see a number of machines in the air, three below and two above us, circling about like hawks. And, like soaring birds, these machines had their air-lanes, designated courses and levels being devoted to the different classes of machines. The landing was made without incident and the hour’s flight was ended.
Outline of Meteorological Work at the Aviation School.—At the close of the lecture detail, the attention of the student aviators was called to the importance of their having as thorough knowledge as possible of the fundamentals of meteorology. The application of these fundamentals to the analysis of air conditions met with in their daily flights was shown to be essential. Investigations as to varying wind direction were taken up by one of the staff instructors by the use of small parachutes to be dropped at different altitudes. (See [Fig. 8].) Through the coöperation of the local official in charge of the San Diego Weather Bureau station, duplicate signal sheets were available from which the student officers made their local weather maps. From these maps and their own flights, they could arrive at some relationship between the actual and the theoretical 3,000- and 10,000-foot level maps prepared from the Bigelow formula, as used by the Bureau. Lectures were given on temperature and its distribution; winds, moisture, and clouds were also made part of the course, one of the papers of the Bureau[I] being reprinted by the aviation school by permission of the Chief of the Bureau and used as a textbook. The Weather Bureau furnished the station with a standard set of meteorological instruments so that the student officers could become perfectly familiar with the regular equipment at the Weather Bureau stations.
[I] “Clouds of California,” Carpenter, 1914, 24, 2d ed., Ft. Leavenworth (U. S. Army Press).
Extending the Usefulness of the Bureau to the Aviators.—Practical utilization by the aviators of this district of the information possessed by the Bureau has received considerable impetus during the past six months. During the cross-country flights of April and May, 1916, the Los Angeles station was directed by the Chief of Bureau to furnish weather and flight conditions between San Diego and Los Angeles. With the aid of the general weather-map data from the regular stations, and special observations of wind, weather, and fog conditions on the immediate coast near Los Angeles, and on Mount Wilson, it was possible to issue satisfactory forecasts of flying conditions. The eye-observations of fog-heights as determined by the Weather Bureau coöperative station at the Mount Wilson Solar Observatory were especially valuable. From this mountain (6,000 feet elevation) it is possible on a good day to see the whole length of the coast from Point Firmin, San Pedro harbor to Point Loma, San Diego Bay. Knowing different levels, the observer at Mount Wilson was able to give actual thickness and extent of the fog-belt and its past twenty-four-hour history.
CHAPTER IV
INVESTIGATING THE UPPER AIR
Balloon Soundings into the Stratosphere.—It was the writer’s privilege to be present when some highly interesting and instructive experiments made by the Weather Bureau in coöperation with the Smithsonian Institution, in sounding the upper air were made at Avalon, Santa Catalina Island, off the coast of southern California in July and August, 1913.[J] The results of this work were in close agreement with similar soundings of the upper air throughout other surveyed portions of the earth’s atmosphere, and a record ascension for this country was made on July 30—32,643 meters or 20½ miles. In common with other observations of temperatures in the stratosphere, the minimum temperature of these soundings (-90 F., August 3) was registered within the first 10 miles.[K]