_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] [J] University of California Chronicle, 1915, 17:1–25, Berkeley. [K] Monthly Weather Review, 1914, 42:410, Washington. Of especial interest to the aviator is the table on the next page which shows wind velocities increasing with elevation as determined by observations of the Avalon balloons. RECORD OF AVALON ASCENTS, JULY-AUGUST, 1913 _Table showing Theodolite observations of wind velocities (meters per second) at elevations of 1,000 and 5,000 meters_