Probably prior to WW 1. The .22 Velodog was replaced by the .2 LR and the .25 Auto cartridge. It is a pity, but "Janssen et Fils Co." at Rue Lambert-Le-Begué of Liege, Belgium only worked from 1893 to 1939; WWII interrupted business and after it, from 1946 to 1957 went under a low-activities period, closing since then. They made nice shotguns, rifles and handguns. Janssen et Fils Cie of course means Janssen and Sons Company.
Nice revolver
50-150 USD
20-80 usd
50-1000 usd
50-500 usd
60 or so
Pi Squared
50-1000 usd
A Colt .357 Mark III nickel plated revolver is worth between $500 and $750. The actual value varies greatly based on the gun's overall condition.
$ 150
50-500 USD or more depending on EXACTLY what you have.
With the brief description that you have supplied,I would say that you have a SMith and Wesson model of 1905 4th change revolver.