The Collaborative International Dictionary of English v.0.48:

Verner's law \Ver"ner's law\ (Philol.)
   A statement, propounded by the Danish philologist Karl Verner
   in 1875, which explains certain apparent exceptions to
   Grimm's law by the original position of the accent. Primitive
   Indo-European k, t, p, became first in Teutonic h, th, f, and
   appear without further change in old Teutonic, if the accent
   rested on the preceding syllable; but these sounds became
   voiced and produced g, d, b, if the accent was originally on
   a different syllable. Similarly s either remained unchanged,
   or it became z and later r. Example: Skt. sapt[=a] (accent on
   ultima), Gr. 'e`pta, Gothic sibun (seven). Examples in
   English are dead by the side of death, to rise and to rear.
   [Webster 1913 Suppl.]