FIG. 147—Showing how men can work under water.
In many cases men work in diving suits rather than in caissons; these suits are made of rubber except for the head piece, which is of metal provided with transparent eyepieces. Air is supplied through a flexible tube by a compression pump. The diver sometimes carries on his back a tank of compressed air, from which the air escapes through a tube to the space between the body and the suit. When the air has become foul, the diver opens a valve in his suit and allows it to pass into the water, at the same time admitting a fresh supply from the tank. The valve opens outward from the body, and hence will allow of the exit of air but not of the entrance of water. When the diver ceases work and desires to rise to the surface, he signals and is drawn up by a rope attached to the suit.
192. Combination of Pumps. In many cases the combined use of both exhaust and compression pumps is necessary to secure the desired result; as, for example, in pneumatic dispatch tubes. These are employed in the transportation of letters and small packages from building to building or between parts of the same building. A pump removes air from the part of the tube ahead of the package, and thus reduces the resistance, while a compression pump forces air into the tube behind the package and thus drives it forward with great speed.
CHAPTER XIX
THE WATER PROBLEM OF A LARGE CITY
193. It is by no means unusual for the residents of a large city or town to receive through the newspapers a notification that the city water supply is running low and that economy should be exercised in its use. The problem of supplying a large city with an abundance of pure water is among the most difficult tasks which city officials have to perform, and is one little understood and appreciated by the average citizen.
Intense interest in personal and domestic affairs is natural, but every citizen, rich or poor, should have an interest in civic affairs as well, and there is no better or more important place to begin than with the water supply. One of the most stirring questions in New York to-day has to do with the construction of huge aqueducts designed to convey to the residents of the city, water from the distant Catskill Mountains. The growth of the population has been so phenomenally rapid that the combined output of all available near-by sources does not suffice to meet the increasing consumption.
Where does your city obtain its water? Does it bring it to its reservoirs in the most economic way possible, and is there any legitimate excuse for the scarcity of water which many communities face in dry seasons?