Source : Webster's Revised Unabridged Dictionary (1913)

Microcrith \Mi`cro*crith"\, n. [Micro- + crith.] (Chem.)
   The weight of the half hydrogen molecule, or of the hydrogen
   atom, taken as the standard in comparing the atomic weights
   of the elements; thus, an atom of oxygen weighs sixteen
   microcriths. See {Crith}. --J. P. Cooke.