Recently I acquired a door bell. It has a 5 inch diameter brass dome that screws onto an iron frame with iron bits making a ringing mechanism. On the outside rim of the brass dome there is an inscription that reads “P.&W.Co. PATENTED AUG 11, 1868”.
I have done some research about this bell and from that I understand there were at least two slightly different versions made. The second version had the inscription “PATENTED AUG 11, 1868”; excluding the “P.&W.Co.”
The internal mechanisms of each version were very similar but with subtly differences. They both included a crank that was used to turn a cog wheel which in turn moved a rocker with a spring. The rocker drove one of two hammers against the brass dome.