Hi falonseve......welcome to TFF.
EASTERN ARMS CO. was a tradename used by Sears Roebuck & Company on revolvers made by Meriden Firearms.
Meriden Arms was actually owned by Sears, and manufactured a line of top-break revolvers and shotguns in the 1905 to 1920 timeframe.
The Meriden revolvers closely resembled the Iver Johnson revolvers of the time because the plant manager at Meriden, Andrew Fryberg, had previously worked for Iver Johnson.
The caliber of your revolver should be marked on the barrel, but most of these revolvers were made in .32 S&W and .38 S&W.