(Note: The links to figure 1, figure 2 and figure 3 are active)
Written in 1939 by W. H. Wright
On Sunday evening, May 21, 1939, at about 7:11 p.m., an Army airplane (Douglas A-17) collided with the main building of the Lick Observatory. The plane was of the "attack" type and was said to have been capable of a speed of 200 mph; it was piloted by Lt. Richard F. Lorenz and carried Private W. E. Scott as a passenger. Both occupants were instantly killed. Mt. Hamilton, on which the observatory stands, was enveloped in clouds at the time. The plane belonged at March Field near Riverside (California) and was returning there from Hamilton Field near San Francisco, when it struck us. Mt. Hamilton is in a direct line between the two stations, and this line bears south east, so that the plane was on its course at the time.
The plane struck the west facade of the building, about 50 feet north of the principal entrance, and crashed through two offices into the main observatory corridor, where it was stopped by the reinforced concrete wall which forms the east side of the building. The direction of motion within the building was, as nearly as can be determined, southeast. In its course the plane penetrated to brick walls, one 20 inches and the other 13 inches in thickness, and went diagonally through a dividing wall separating the two offices.
The engine and greater part of the fuselage was deposited in the offices and corridor, with bricks and mortar from the demolished walls. Figure 1 shows the area of entry. The protruding fragment is the right wing. Figure 2 is a view of the main observatory corridor looking toward the north, and figure 3 is from the other side of the wreckage, looking south. The pile of debris-plane, bricks and mortar-was 40 feet long and nine feet high at the crest. It required two or three days to clear this material away and to wall off the damaged section of the building for the purpose of excluding dust. After that it was possible again to take up normal activities at the observatory.
When we turn from the contemplation of the tragic consequences of the accident it is possible to derive some satisfaction from the circumstance that little or no damage was done to the scientific equipment or to photographic and other records of the observatory. The material loss is, of course, considerable, but it is believed that this will not prevent speedy rehabilitation of all the observatory's facilities.
Records of the effect of the impact of the plane are given by our seismographs and self-recording barometers. Of each of these instruments we have two types, but at the moment only one seismograph and one barogram are available for study.
The seismogram, which is from the Wiechert machine, has been examined by Dr. Jeffers and myself. The record of the disturbance appears, to the eye, as a small spot on both the West-East and North-South tracings. Examined with a glass the spots are readily seen to be minute "shock" records of about two or two and a half seconds duration. The initial movement is in each case about 1 mm, followed by a rapid swing to a point .4 mm on the opposite side of the zero point; subsequent oscillations are not readily distinguishable, but the trace is broad during the remainder of the short interval of time above indicated. After allowing for the magnifying factor of the instrument, and otherwise reducing the data to simple terms, we find the following facts. There was a sudden displacement of the earth, at the site of the seismograph, toward the south east, about 1/57 mm in amount. This was followed by a reverse movement totaling approximately 1/41 mm, or .001 inch, after which the vibration gradually died out. The initial displacement corresponds, as would be expected with the direction of the flight of the airplane, that is to say from northwest to southeast. The seismograph is distant about 120 feet (36 meters) east-north-east from where the plane struck, so it is clear that a very considerable part of the mountain top was set in motion by the impact. The time of the initial displacement was 10 minutes and 59 seconds past 7 p.m., Pacific Standard Time. This figure is regarded as possibly subject to an error of a second or two; it furnishes the most reliable time of the collision now available.
The barogram to which reference has been made is that provided by the Draper mercury-weight self-recording barometer. There was a sharp barometric rise of about .013 inch and an immediate recovery. In view of the weight of the moving parts of this barometer and the short duration of the disturbance, it is probable that the actual rise in pressure was considerably in excess of the above amount. It should be stated that the barometer is situated in the observatory corridor and that some increase in pressure would be expected as a consequence of the sudden entry of the plane into the building and of the falling inward of the walls.
At the time of the accident there was one person in the building and some half dozen in the immediate vicinity. Everyone remarked (about) the roar of the approaching plane, which was obscured by the cloud in which the mountain was enveloped. The noise of the impact seems to have been effectively smothered within the building, and the single occupant mentioned did not at first realize that the building had been struck. The sudden silence following the roar of the engine indicated to all that the plane had "crashed", but, until the opening in the wall was discovered and the mutilated machine found in the observatory corridor, it was believed that the accident had occurred somewhere on the mountain side.
It may be worth relating that two visitors were just arriving at the observatory when the plane flashed across their path and buried itself in the building. Until matters were explained to them they apparently had no very clear idea of the meaning of it all. Possibly they regarded it as a mere matter of observatory routine.
As will be realized, the situation precipitated by the collision was a very serious one. Within a few seconds of time a great mass of gasoline-soaked wreckage established itself within a far-from-fire-proof building. The cool and efficient manner in which the young man and women who were first on the scene adopted precautions against explosion and fire are deserving of the highest commendation. Their prompt and efficient action undoubtedly saved the observatory from a major catastrophe
Written in 1939 by W. H. Wright.