The Collaborative International Dictionary of English v.0.48:

Microcrith \Mi`cro*crith"\, n. [Micro- + crith.] (Chem.)
   The weight of the half hydrogen molecule, or of the hydrogen
   atom, at one time taken as the standard in comparing the
   atomic weights of the elements; thus, an atom of oxygen
   weighs sixteen microcriths. This unit is no longer used, and
   has been replaced by the Dalton, which is of approximately
   the same value. See molecular weight and Crith. --J. P.
   Cooke.
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Dalton \Dalton\ n.
   John Dalton, scientist, born 1766, died 1844.

   Syn: John Dalton.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

dalton \dalton\ n. [from the chemist John Dalton, proponent of
   the modern atomic theory of matter.]
   a unit of mass, approximately 1.66 x 10^-24 grams; -- it is
   approximately equal to the mass of one hydrogen atom, but the
   exact value differs slightly as used in physics and
   chemistry. It is used mostly to describe the size of proteins
   and nucleic acids in biochemistry.

   Note: Molecular weights are often expressed as dimensionless
         units, the unit being understood (in chemistry) to be
         the atomic mass unit with carbon equal to 14. Thus
         having a "molecular weight of 255" means the same as
         each molecule having a mass of 255 daltons.

   Syn: Syn. atomic mass unit.
        [PJC]

WordNet (r) 3.0 (2006):

Dalton
    n 1: English chemist and physicist who formulated atomic theory
         and the law of partial pressures; gave the first
         description of red-green color blindness (1766-1844) [syn:
         Dalton, John Dalton]