Permissive working allows more than one train to be in a block section at one time but trains must be run at low speed in order to stop on sight behind the train in front. Such working is often authorised to allow freight trains to bunch together to await a path through a bottleneck instead of being strung out over several block sections, as would be necessary if absolute working were in force.

I am the true vine, and My Father is the vinedresser.

Sensory fibers ranged in adaptation to the mechanostimulus as fast-adapting, slow-adapting, or on-off (i.e., promptly adapting), indicating the presence of three types of mechanoreceptors.

By 1830, more than two million tons of coal a year, principally from the North East, arrived in London by coastal collier, and that figure reached three million tons by the 1840s.