Source : Webster's Revised Unabridged Dictionary (1913)

Twaddell \Twad"dell\, n., Twaddell's hydrometer \Twad"dell's
hy*drom"e*ter\ [After one Twaddell, its inventor.]
   A form of hydrometer for liquids heavier than water,
   graduated with an arbitrary scale such that the readings when
   multiplied by .005 and added to unity give the specific
   gravity.