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Rh as a much more positive circulation of air to the separate rooms can be secured than by the other method.

The system shown in Figure 48 is interesting also on account of the construction of the main cold-air duct and the connections from it to the radiator boxes. These are well illustrated in Figure 49, the main duct, it will be noted, being of brick, and underground. In the author's opinion there is one particular in which the system shown in Figure 48 might have been much improved. The cold-air duct is long and winding, and had it been more uniform in size

Figure 48.—The Indirect System in a Philadelphia Residence.

and supplied with another cold-air connection on the side of house opposite the existing one, it would have insured a more positive circulation to all the radiators. The reason of this is that in cases, such as shown in Figure 48, where there is only one cold-air connection for a number of radiators, when there is a strong wind blowing against the side of the house opposite the fresh-air inlet it is sometimes very difficult to get a good draft in the flues, especially in those most removed from the cold-air inlet, as the force of the wind (which, with the best constructed houses, blows through the walls to a great extent), seriously opposes the current