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kronstadt21:

Patent for an ultra-hard core vibrator from 1937, euphemistically described as being used for,   'the vibration of solids, liquids or gases, either by means of a direct action of the vibrating device upon these or by the intermediary of suitable arrangements such as membranes, screens, molds, chutes, jigging tables, etc., to which the vibrating device is connected. In particular are these vibrating devices suitable as internal high frequency vibrators for placing concrete'.
Source: Google Patents

kronstadt21:

Patent for an ultra-hard core vibrator from 1937, euphemistically described as being used for,
  'the vibration of solids, liquids or gases, either by means of a direct action of the vibrating device upon these or by the intermediary of suitable arrangements such as membranes, screens, molds, chutes, jigging tables, etc., to which the vibrating device is connected. In particular are these vibrating devices suitable as internal high frequency vibrators for placing concrete'.


Source: Google Patents