the sinker to pass swiftly to the bottom. While the apparatus for sounding the sea consisted of a weight secured to the end of a hempen cord which was paid out from a simple reel on the deck of a vessel, no reliability could be attained in the measurement of depths, because the cord employed was necessarily so large as to become a controlling element in the weight of the system. But when the project for the Atlantic telegraph cable made it necessary to obtain accurate measurements of the depth of the ocean, Midshipman Brooke, of the United States Navy, took the first great step in providing means for trustworthy deep-sea sounding by inventing an implement in which the sinker, enveloping a tube secured to the sounding
Fig. 4.—The Sigsbee Deep-sea Sounding Machine.
line, was detached on striking the bottom and left behind when the tube was drawn up.
The modern form of deep-sea sounding cylinder, which is the result of the experience of Commander Sigsbee, of the United States Navy, during his great work in developing the orography of the Gulf of Mexico, is provided with valves at the upper and lower ends which open upward, and during the descent allow
