Page:Popular Science Monthly Volume 47.djvu/628

612 by Mr. Alvarado Mayer, a member of the Detroit Fire Department, in 1809. Mr. L. D. Shaw, of Boston, also introduced a successful valve in 1874. Since then there have been a number of different valves in use. Mr. Cornelius Callahan, of Canton, Mass., perfecting one in the neighborhood of 1888. These three are about the only ones in general use to-day.

It has been seen that the first ladder trucks were introduced at the beginning of this century, and the patterns then adopted have been followed more or less to the present day. Portable escapes were invented by the score, some in the form of extension ladders, others as lazy tongs, and others in the form of cranes, by which a bucket could be raised and lowered. None of these came into general use, because they had not reached a stage of development at which apparatus of that nature could be made light and strong enough to be practicable. The ordinary ladder truck consists of a long frame, with crossbars at different heights provided with rollers. These are equipped with several ladders of different lengths, and an extension ladder. The latter is a combination of ladders that slide over each other by means of a chain and pulley. The whole length is rested against a building, and the center is supported by props. The Bangor Extension Ladder Company and several others make ladders of this kind. The Gleason & Bailey Manufacturing Company, the Stewarts, C. T. Holloway, Seagrave & Company, P. J. Cooney, and some of the engine-makers, manufacture ladder trucks that differ simply in minor details too numerous to describe.

The aërial truck consists chiefly of an extension ladder that rests on trunnions on a turntable at the forward end of the truck. The extension ladder is raised in much the same manner as is the water tower, and when erect is capable of supporting itself with several working firemen without resting against a building. The Hayes, the Gleason & Bailey, the Arrow, and the Babcock are among those well known. The aërial trucks carry a full complement of ladders.

The largest ladder trucks are provided with a steering wheel over the rear axle to facilitate the turning of corners, and Mr. Steck, of Chicago, has invented a depressed rear axle which lends stability to the truck, while a lever in place of a steering wheel directs the rear wheels.

In addition to the regular ladders, a variety of apparatus is carried on every truck. The axes, or hooks as they are called, are too well known to need description. In olden times large, heavy hooks were used to tear down buildings, but these have since been abandoned. It is interesting to note in this connection that as late as 1857 the Scientific American published an illustration of an enormous hook mounted on wheels. The hook was intended