Retrospective.---The past twenty years has witnessed important and essential improvements in the arrangement of the parts of fire hydrants. The same twenty years has witnessed also the more general introduction of high pressures into public water services, and the more general construction of water-works in northern cities, where the hydrants are subjected to severe tests of deep penetrating frost, and the expansions of earth frozen fast to their cases.

In the year 1800 we find the "fire-plug" of London, a simple branch, turned upward upon the top of the main, enlarged slightly within from the main upward, so that a stand-pipe with nozzle, which was carried by the fire-brigade, could be inserted as occasion demanded. When the stand-pipe was withdrawn, after use, a conical plug of wood, with handle extending to the surface of the ground, was inserted to keep dirt and rubbish from falling into the pipes. Water was shut off from these hydrant branches except during fires, and while the stand-pipe was in place.