This is the patent for the Protean gear, a system using an expanding chainwheel to vary the gear ratio.
One of the interesting things about this patent is the passage starting at line 39 on page 2:
“As the wheel expands and contracts the chain will become tight and loose and we therefore provide pulleys or rollers mounted on spring levers to take up the slack in the chain. The particular arrangement we prefer is a lever fulcrated near its centre with a roller at each end and the chain passing over one roller and under the other. We use a spring with this arrangement so as to keep a constant tension on the chain.”
This is often considered to mark the invention of the sprung pulley cage that is such an integral part of all modern derailleurs.