On friction: its simple and composite kinds
Simple rubbing generates fire; oiliness, wheel-axles and rolling balls ease it
This text page, headed 'On friction', classifies the kinds of rubbing motion. Simple friction is when a body is dragged over a plain surface with nothing interposed, and this alone can generate fire, as happens in a water-wheel between the iron and the wheel once the water is taken away. Composite friction divides in two: one where an oiliness of some subtle body is interposed between the rubbing bodies, and one where a further friction is interposed, such as the friction of the axles of wheels, which itself subdivides into the interposed oiliness and the use of balls and the like.
On this page
Simple friction generates fire
Friction motion divides into a simple kind and composite kinds. The simple is when a thing is dragged over a plain surface with nothing interposed; this alone, when strong enough, generates fire, as is seen in water-wheels between the iron and the wheel once the water is removed.
Composite friction: oiliness, axles and balls
Composite friction divides in two: one where an oiliness of some subtle body is interposed between the rubbing bodies, and one where a further friction is interposed, such as the friction of the axles of wheels. The first is again subdivided into the interposed oiliness and the use of rolling balls and the like.