The Collaborative International Dictionary
Bathometer \Ba*thom"e*ter\, n. [Gr. baqo`s depth + -meter.] An instrument for measuring depths, esp. one for taking soundings without a sounding line.
Wiktionary
n. An instrument that measures the depth of water, used especially to measure the depth of ocean water.
Wikipedia
A bathometer (also bathymeter) is an instrument for measuring water depth. It was previously used mainly in oceanographical studies, but is rarely employed nowadays. The term originates from Greek βαθύς (bathys), "deep" and μέτρον (métron), "measure".
Usage examples of "bathometer".
Manda came also with one or two of his comrades, examining with the greatest interest the bathometer and thermometer with the other instruments which were attached to the wall.
Marianna looked at what Alex had told her was the bathometer and realized they were indeed going down.