What is a half watch; a watch of two hours, of which there are two, the first dogwatch from 4 to 6 o'clock, p.m., and the second dogwatch from 6 to 8 o'clock, P. M. Totten called?

dogwatch — A half watch; a watch of two hours, of which there are two, the first dogwatch from 4 to 6 o'clock, p.m., and the second dogwatch from 6 to 8 o'clock, P. M. Totten. (Webster's 1913.)