Waltham 1894 model, grade 225

The mainspring is the one wearable part in a vintage watch. If well cared for an serviced, everything else in a watch will last indefinably But mainsprings will eventually break or "set" (where they start to hold their compressed shape).

Later alloy springs are much better about these troubles, but early springs always have to be replaced sooner or later.

This movement is a Waltham 12 size, 17 jewels, 1894 model, grade 225.  It features this effective, but a little tricky to assembly, "shipper" mechanism for winding/setting, or "keyless works". Folks taking one of these apart without being familiar with it are always losing that semi-circular shipper spring.