This item was found on Steve's Gas Engine Shed website, which is accessible at http://www.oldengineshed.com/motsinger.html
The Motsinger Auto-Sparker Dynamo
built by The Motsinger Device Manufacturing Co., Pendleton, Indiana
Patented in 1900, this little dynamo was an after market "battery eliminator" for any engine using batteries for a low tension ignition system. The ingenious method of speed governing on these units allowed the engine to be both started and run solely on the Motsinger's output. As can be seen in the picture, the small flyball governer on the left side actuates a simple spring loaded mechanism that pivots the entire dynamo away from the flywheel, thus allowing the drive wheel to slip and slow down. A constant speed was maintained by the amount of slip allowed. During starting, there would be little or no slip, since engine cranking speed is slower than running speed. The Motsinger's output would be at maximum to allow starting without battery assist. Once the engine started, the Motsinger's governor would prevent it from overspeeding.
Motsinger on Associated Chore Boy engine
A Typical Igniter and How It Works