The Science Museum - Gradient

The Science Museum - Gradient main image

I find it difficult to separate out Edmund Hodgkinson’s various designs, and this picture is particularly indistinct. The Science Museum describes it as a “three-speed gear, patented by E. H. Hodgkinson between 1896 and 1899, (which) was exhibited on a bicycle at the Starley Show in 1899” - so this seems to be the final 1899 version. The Science Museum goes on to explain:

“Gear changing in accomplished by first rotating the pedals backward, causing a flexible metal strip to rotate two segmental pieces about the rear hub, which engage with the edge of the chain and lift it clear of the back sprockets, a spring jockey pulley permitting the necessary play in the chain.

Three hub sprockets, which are mounted together and are free to slide laterally on the rear hub, which they drive by means of a ratchet, are then moved by a selector quadrant lever mounted on the frame top tube, so as to bring the drive sprocket into line with the chain.

On again (pedaling) forward the segments are spring returned to the clear position, allowing the chain to mesh with the (selected) sprocket.”

This photo is licensed under the Creative Commons Attribution 3.0 License.