1. An instrument used to illustrate the fact that in a vacuum liquids and solids fall at the same rate. It consists of a hermetically sealed tube exhausted of air and partly filled with water. When the tube is quickly reversed, the water falls on the end with a noise like that of a hammer.
1805. Nicholson’s Jrnl. Nat. Philos. (80), XI. 217. The water-hammer. This instrument, which is made and sold by the glass-blowers and barometer-makers, consists of [etc.].
1870. Tyndall, Heat, iv. § 131 (ed. 4), 112. One effect of the withdrawal of the elastic buffer [i.e., the air] is, that the water falls with the sound of a solid body, and hence this instrument is called the water hammer.
attrib. 1881. Tyndall, Ess. Floating-Matter of Air, iii. 147. A number of hermetically-scaled tubes charged with the same infusion … have maintained for more than a year … their water-hammer sound.
2. Hydraulics. The concussion or sound of concussion of water in a pipe when its flow is suddenly stopped, or when live steam is admitted.
1891. Century Dict.
1910. Encycl. Brit., XIV. 67/1. [Hydraulics] If in a pipe through which water is flowing a sluice is suddenly closed so as to arrest the forward movement of the water, there is a rise of pressure…. This action is termed water hammer or water ram.
1919. ‘Klaxon,’ in Blackw. Mag., Feb., 183/2. There came a bubbling roar from the vent of A, well forward, and then the clang of a heavy ‘water-hammer’ in the pipe as the tank filled.
b. Path. Water-hammer pulse, a jerky pulse with a full expansion, followed by a sudden collapse.
1899. Allbutt’s Syst. Med., VI. 388. The well-known ‘water-hammer pulse’ or ‘pulse of unfilled arteries’ of aortic regurgitation.
3. Surg. A metal hammer heated in boiling water, used to produce a blister by gently striking the skin.
1891. Century Dict.
1911. Webster.
