Definitions for "Bathythermograph"
A brass torpedo-shaped device measuring about 36 inches long by four inches wide that sonarmen lowered from a boom on the fantail (in all kinds of weather). The temperature versus depth was etched on a smoked glass slide. This data was used to calculate sonar ranges and was done every watch.
an instrument that is lowered into the sea and records temperature and depth as a single trace.
a device reeled over the side which measures temperature variation with depth