This is an ad from the back cover of Science Gossip magazine, a publication which I discovered via Nemfrog. These “hot-air motors” were made by “JOHN J. GRIFFIN & SONS, Ltd, Chemical, Philosophical, and Photographic Instrument Makers, MAKERS TO THE ADMIRALTY, WAR DEPARTMENT, INDIA AND COLONIAL GOVERNMENTS, physical and chemical apparatus of every description.” The motors have no noise and no smell, and are invaluable in a laboratory or workshop. Invaluable for what? I guess you put a spirit-burner inside one (a lamp burning… alcohol? methanol maybe) and the heat made the wheel go around, giving power to some belt-driven device of your own.
The same page has another ad for Watson’s microscopes and holoscopic eyepieces.