Definition of "vacuously"

Here, in distress that was consternation, and in fear that was panic, excitedly bobbed up and down a cowboy in bearskin chaps, vacuously repeating the exclamation, "Oh God! Oh God!" […]

1915, Jack London, The Little Lady of the Big House

He scowled vacuously, keeping at bay a horrible enlightenment on the mechanism of effort, which must drive into being a resistance equal to itself.

1938, Norman Lindsay, Age of Consent, 1st Australian edition, Sydney, N.S.W.: Ure Smith, published 1962, page 211