RADIATORS.--Much time and money has been spent in developing a simple and efficient type of radiator. As, of necessity, it must be made up of a multiplicity of parts, leakage is apt to occur, and while in the past most of the constructions depended on soldering together the various portions, it will be seen how insecure such a system of construction must be necessarily. CONSTRUCTION OF RADIATOR.--In Fig. 75, is shown a front and a sectional view of portion of a simple type, which is made up of square tubes A, their ends being fitted into square holes formed through front and rear plates B C, and the tubes are so arranged that there are small spaces D between the tubes. [Illustration: Fig. 75. Radiator Type.] When water enters through the inlet tube E, it fills the spaces, and being cooled moves downwardly, while the air rushing through the open-ended tubes, cools down the water over the large area thus afforded. All radiators employ substantially the same construction, the illustration given being merely to show the principle of the device. A drain cock G, Fig. 74 should be placed in the system below the radiator, in the pipe line B, so that water can be drained off from all the pipes, to prevent liability of freezing. The diagram shows the fan shaft connected and run by a belt H. This is not the best construction, as it is not a positive drive. Most cars are provided with gearing for this purpose. OPERATION OF RADIATOR.--The water is thus carried from the bottom of the radiator to the water jacket space, and from the upper end of the jacketed area to the top of the radiator, and used over again. More or less of the water is lost by evaporation, so more must be added from time to time, and the radiator should be kept as full as possible to get the best results. If the water level falls too far below the return pipe at the top of the radiator, the area of the heating surface and the decreased quantity of water exposed to the cooling surface, are likely to cause undue heating, or vaporization. THE PUMP.--A variety of pumps are used, but they are generally based on the principle of the turbine impelling system, or on centrifugal action. A type which utilizes both these principles is shown in Figs. 76 and 77, in which the former is a cross vertical section of 77 along line 1, and the latter is a central vertical section on line 2 of Fig. 76. The device comprises a cylindrical shell A, with an inlet B, at one edge near the front wall, and an outlet C at the upper edge near the rear wall. PUMP CONSTRUCTION.--Within is a revoluble tubular hub D, with one end E projecting, to which power is applied. A disk partition G is secured to this hub, midway between its ends, and on each side of the partition is a pair of oppositely-projecting convolute blades, those on the inlet side, indicated by H, and the ones in the discharge side by I. [Illustration: Fig. 76. Side View of Pump.] [Illustration: Fig. 77. Section.]