There were one hundred and sixty-four patents examined, and out of this mass, twenty-nine were selected as bearing directly upon the Change Gear problem; the others being for forms of variable speed devices and similar inventions, not properly coming under the head of the Evolution of the Change Gear. These twenty-nine patents have been very carefully considered and described, their special or distinguishing features illustrated and compared in a conscientious and disinterested manner, which it is hoped, will prove both instructive and useful to those who may be interested in this field of mechanical development.