Abstract: A fluid is admitted into a bath having a certain temperature. The temperature of the fluid is different from that of the bath. The fluid travels through the bath so that heat transfer occurs between the bath and the fluid while, at the same time, the bath is thus caused to be agitated. The flow of the fluid into the bath is regulated in such a manner as to maintain the temperature of the bath within predetermined limits. A preferred application resides in the cooling of a bath, particularly one which is used for the heat treatment of steel wire which has been hot rolled immediately prior to the introduction thereof into the bath. Here, the fluid may be in the form of a gas upon being admitted into the bath. Alternatively, the fluid may be in the form of a liquid which vaporizes at the temperature of the bath. In this event, heat is removed from the bath partially in the form of the heat of vaporization of the liquid. It is also possible to feed both a gas and a liquid into the bath.