Instruments \ Seismic \ Seismographs \ 

Description:


Used on the ocean bottom for detecting, measuring and recording seismic events generated by explosive detonations. Heavy case enclosed the seismograph and withstood pressures to 10,000 PSI. This is one of the ocean bottom seismographs that was designed and built completely by Ewing, Worzel and Vine about 1937.

Items #61a and b are the two parts of the pressure case made out of 71ST aluminum which is designed to stand pressures up to 10,000 psi which is anywhere in the ocean basin except in the great deeps themselves. Item 61c is the package (Addendum: By private communication with Worzel, this seismograph was built by Allan Vine, J. L. Worzel and Maurice Ewing at Lehigh University in 1934.) It has a Hamilton Watch which fits into the holder in the little cylindrical case which turns the instrument on at a precise second. When the precise second comes up on the watch the power is provided to the relay which starts the motor that drives the camera in the black case in the one end and turns the light on that provides light for the reflection to the galvinometer which was also built by Ewing, Worzel and Vine. The galvinometer mirrors returned the light into the camera. Between the watch case and the galvinometer is the amplifier which amplified the signal coming in from the geophone and above that is the tuning fork which provided timing lines on the records so that timing could be obtained. On the far side are two cylindrical tubes which contained regular flashlight batteries which provide power for the light and the motor that drove the camera. The ocean bottom seismographs were used three such units at a time, placed about 1,000 feet apart so that each of the units was made up of a float consisting of approximately a 10 inches neoprene tube which was about 12' long and contained gasoline for flotation. To the top of the float was added a bamboo pole with a flag so that it could be easily located when it returned to the surface after use. Attached to the instrument case, was a triangle made out of bamboo which held a geophone off to the side of the case so that the geophone would land about 6' away from the instrument case. Directly beneath the case was a rock salt container that would not be opened into the flow of water until the instrument was on bottom. Below the rock salt container was about 30 lbs. of cast iron balast. The system of using these would be to put one of these instruments over move about 1,000' on a line, put a second one over move on 1000' on a line, put a third one over and then move out another, probably 500', and put down a somewhat similar unit that would also have a Hamilton Watch to start it which would fire a bomb, and the bomb was arranged to lied far enough away from the instrument so that it would not blow the instrument up. Then another 1000' beyond that would be a second bomb and probably 1500' beyond that would be a third bomb.

This was the technique for using it. All of the oscillographs would turn on as near to the same second as it was possible to organize them, then as soon as the camera was running, the nearest bomb shooter would fire its bomb allowing time, say about 5 seconds, for the sound waves to travel. The second bomb shooter would then fire and allow perhaps 10 seconds for the sound waves to travel and then the third bomb shooter would fire. Each of the oscillographs could run for about 30 seconds before running out of paper. When the bomb shooters fired, the balast was blown off those machine, and they would immediately start for the surface. The salt releases would operate 5 to 10 minutes after the conclusion of the operation and the 3 oscillographs would then float to the surface. The ship would then look for them on the surface about an hour and a half later as it took about that length of time to make a trip from 2500 fathoms, about the normal depths that we would use them. These were built about 1937 and were used in 1938, 1939 and 1940, but only 2 usable records were obtained in that period. A record is reproduced in the Recent Results in Submarine Geophysics paper that has been left with you also.

Hamilton Pocket Watch

When we first got the crystal chronometer, after Ewing's first cruise with the chronometer; we said this was a great instrument and we contacted Bill Bennett and suggested we bring it down and compare it to the short pendulum clock they had at Hamilton that they rated all their clocks at. He said by all means come along so we took the crystal chronometer down there and set it up before the factory opened in the morning and when the factory opened the time went way off and then it came back on. In the evening when they shut down the same thing happened. They had never known this. What happened was when all their people came to work and turned on their time comparison machinery, it put a surge into the short pendulum clock and the pendulum clock recovered after a while and the same think happened in the evening. They had not known this and were writing their clocks and watches in that period so they were migrating a number of their instruments. They quickly went to work and fixed it so it did not happen anymore. This was sort of a side issue of our use of the crystal chronometer. The Hamilton Watch Company was somewhere in Pennsylvania. The accuracy of a railroad watch was on the order of one part in one hundred thousand and a part in a million would be one second per month so it would be about 10 seconds per month for a railroad watch.

The Hamilton Watch Company gave us the watches, we took the hands off, built the circular dials with the contacts on them and fastened the contacts onto the watch and brought leads out to the side of the watch for making contacts. This was done at Leheigh and Maurice Ewing did most of the work. Professor Wilson at Rice University said he was a great theoretician, but he would never make an instrument man and yet he built these instruments. He had very big hands, very broad fingers, etc. , but yet he built those very fancy parts and put them together and made them work. When Craig Ferris went through LDGO he told him the story that Wilson wrote him a letter of recommendation which he now has and Wilson told the prospective company that he went to work for don't let him near any laboratory equipment, he will tear it up. Maurice said here's these old hands that has built equipment that's gone to the moon and the head of the department said don't let him near anything.