Soundings
We could see that it would be a matter of great and special interest if we could take soundings where we landed, and, discussing it fully, we came to the conclusion that we ought to be able to get sounding materials with a reasonable weight. We got into communication with the Behm Echolot Factory in Kiel, and all our difficulties were immediately brushed aside. After I had been to Kiel and talked over the matter with Herr Behm an excellent apparatus was made and placed gratis at our disposal. (As there were great depths in the district where we were to land, it was not necessary to take the depth to the nearest meter, but we could make an approximate registration. The weight of the whole sounding equipment, with cartridges for a number of charges, was cut down to a few kilograms. There was therefore no obstacle in the way of our taking it with us in the flying machine—and we could also have taken it with us even had we had to make a march towards land.)
The principle was simply as follows. A watertight microphone was sunk about four meters down in the water of a crack in the ice. The microphone was attached by a line to an ordinary head-microphone, which the observer wore. At a distance of twenty-five to fifty meters from the observer a little charge was sunk under the surface which contained ten grams of trinol and was provided with a detonator. The charge was exploded by an electric spark. The observer set a stop-clock going when he heard the explosion, stopping it as soon as he heard the echo from the sea bottom.
On May 28th we took two soundings immediately after each other, and in both cases the stop-clock’s time proved to be five seconds. As sound travels in sea-water at the rate of 1,500 meters per second, the distance from the surface down to the bottom and up to the surface again is equal to 7,500 meters, and thus the sea’s depth is at this place half the amount, namely, 3,750 meters. The echo was quite sharp and not to be misunderstood. Therefore during a later drift, as we did not move far from the place where we had taken the first sounding, we took no more. We wished to reserve the spare charges for a possible march.