THE SUBDIVISION OF A CURRENT OF HOT GAS 89 FIG. 47. indicated in Fig. 47. From the preceding, it may be readily seen that a current of hot gas which i$ giving off heat or cooling cannot be subdivided into equal ascending currents. When, however, the attempt is made to subdivide the current of gas Q into two equal descending currents (Fig. 46), it will be completely suc- cessful. Assuming, for example, that the temperature of one of these currents, q\, should become less than the tem- perature of the current q%. In this case the weight of the column of gas qi will be increased, and the velocity of its descending motion will be in- creased. The current of gas qi will become stronger than #2, its tempera- ture will gradually increase and it will finally become equal to #2. It can be concluded from this that the problem of subdividing a current of gas which is cooling or giving off heat into equal descending channels may be solved in a very simple manner, owing to the fact that there is always a tendency for the temperatures of these descending streams to remain uniform. Therefore, if it is desired to sub- divide a current of hot gas which is cooling or giving off heat, into equal streams, it is necessary to give these streams a downward or descending direc- tion of flow] or, in other words, a cur- rent which is cooling may be subdivided into uniform descending streams.^ (1) Accordingly, it is possible to approxi- mate the fractional resistance in the two chan- nels between which the current is divided, when one branch has a higher resistance or a higher heat loss than the other, because the stream of gas divides itself accordingly. In Fig. 43a, such a case is shown. The stream of gas Q is divided into two descending streams q\ and #2, the average temperatures of which are different, being denoted by t\ and /2. The average FIG. 48a.