The mechanical bathythermograph was invented as a tool to understand the temperature layers of the ocean. The torpedo-shaped device was attached to a long cord and dropped off the side of a boat. As it sunk towards the sea floor, an internal needle scratched a line on a piece of glass that represented temperature relative to water depth. For a thermal element it has a xylene-filled copper coil, which actuates a stylus through a Bourdon tube. The pressure element is a copper aneroid capsule that moves a smoked glass slide at right angles to the motion of the stylus. A double analog record is thus obtained as the BT is lowered and recovered. This device was generally replaced by the expendable bathythermograph (XBT). This object is a bathythermograph MK 5. It has a torpedo-shaped body with 6 fins and is in a grey-painted wooden case. The instrument has a fitting for a bathythermographic slide, and a catch release for a pin to mark the slide. The top of the bathythermograph is marked’Hawker Siddeley’ and it was made by S. Until the development of the bathythermograph in 1938, the thermocline (the layer of rapid temperature change between surface and deep water) had not been understood. The bathythermograph was able to show the structure of this layer more readily than could be achieved by measurements using a water bottle and thermometer. Very nice condition comes with the Manual and Box, Please see the photos. Please take advantage of the zoom feature on the photos to judge cosmetics for yourself. All photos are part of the description and were taken from our own products. What you see in the photos is what exactly you receive. If it’s not pictured it’s not included. (Excluding weekends and holidays). Will apply for all. PO boxes, APO, DPO or FPO zip code. Note to Buyers: All the content of the description have been written base on the facts and our best knowledge. Mistakes may happen and might go above and beyond to resolve any issues. We always reply within a few hours. It barely exceed 24 hours to respond. If you receive an item and there is something wrong or you think it’s not Authentic, please don’t worry because you are 100% protected by us! Just send us a message which goes a very long way. We will respond and resolve any issue very shortly. We have passion to serve and give more service to customers, just let us know.