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The bathythermograph, or BT, also known as the Mechanical Bathythermograph, or MBT;〔 is a small torpedo-shaped device that holds a temperature sensor and a transducer to detect changes in water temperature versus depth down to a depth of approximately 285 meters (935 feet). Lowered by a small winch on the ship into the water, the BT records pressure and temperature changes on a coated glass slide as it is dropped nearly freely through the water. While the instrument is being dropped, the wire is paid out until it reaches a predetermined depth, then a brake is applied and the BT is drawn back to the surface.〔 Because the pressure is a function of depth (see Pascal's law), temperature measurements can be correlated with the depth at which they are recorded. ==History== The true origins of the BT began in 1935 when Carl-Gustaf Rossby started experimenting. He then forwarded the development of the BT to his graduate student Athelstan Spilhaus. Who then fully developed the BT in 1938〔Scripps Institution of Oceanography: Probing the Oceans 1936 to 1976. San Diego, Calif: Tofua Press, 1978. http://ark.cdlib.org/ark:/13030/kt109nc2cj/〕 as a collaboration between MIT, Woods Hole Oceanographic Institution (WHOI), and the U.S. Navy.〔http://museum.mit.edu/150/134〕 The device was modified during World War II to gather information on the varying temperature of the ocean for the U.S. Navy. Originally the slides were prepared "by rubbing a bit of skunk oil on with a finger and then wiping off with the soft side of one's hand,” followed by smoking the slide over the flame of a Bunsen burner.〔Letter from Allyn Vine to Richard H. Fleming, 20 August 1941.〕 Later on the skunk oil was replace with an evaporated metal film.〔 Since water temperature may vary by layer and may affect sonar by producing inaccurate location results, bathothermographs (U.S. World War II spelling) were installed on the outer hulls of U.S. submarines during World War II. By monitoring variances, or lack of variances, in underwater temperature or pressure layers, while submerged, the submarine commander could adjust and compensate for temperature layers that could affect sonar accuracy. This was especially important when firing torpedoes at a target based strictly on a sonar fix.〔 More importantly, when the submarine was under attack by a surface vessel using sonar, the information from the bathothermograph allowed the submarine commander to seek thermoclines, which are colder layers of water, that would distort the pinging from the surface vessel's sonar, allowing the submarine under attack to "disguise" its actual position and to escape depth charge damage and eventually to escape from the surface vessel.〔 Throughout the use of the bathythermograph various technicians, watchstanders, and oceanographers noted how dangerous the deployment and retrieval of the BT was. According to watchstander Edward S. Barr: "… In any kind of rough weather, this BT position was frequently subject to waves making a clean sweep of the deck. In spite of breaking waves over the side, the operator had to hold his station, because the equipment was already over the side. One couldn't run for shelter as the brake and hoisting power were combined in a single hand lever. To let go of this lever would cause all the wire on the winch to unwind, sending the recording device and all its cable to the ocean bottom forever. It was not at all uncommon, from the protective position of the laboratory door, to look back and see your watchmate at the BT winch completely disappear from sight as a wave would come crashing over the side. … We also took turns taking BT readings. It wasn't fair for only one person to get wet consistently."〔“MIDPAC — The First Big Step,” manuscript, 17 August 1975.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bathythermograph」の詳細全文を読む スポンサード リンク
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