1879.] CIRCULATION OF WATER IN PIPES. 571 



necessarily the 2.9 oz. goes down and the 2.8 oz. goes up. When the 

 water has been so far transfused as to have become of the same tem- 

 perature throughout, the motion necessarily ceases, because it is all of 

 equal weight. 



Therefore the way to ascertain whether water will circulate in a 

 given arrangement of boilers and pipes, is to take the weight of all 

 which we wish to ascend, and the weight of all which we wish to de- 

 scend, and to ascertain if the weight of the latter exceeds that of the 

 former. If it does, the circulation will be as we wish ; if the opposite 

 is the case, the circulation will be reversed ; and if the weights are 

 equal, there will be no circulation at all. We get the relative weights 

 by multiplying the specific gravity of each portion by the perpendicu- 

 lar weight of that portion, and we get the specific gravity from the 

 temperature. It is not quite exact to take the mean temperature of 

 each portion, but the errors nearly balance themselves, and may be 

 disregarded. We need pay no attention to the portions which are 

 on a level ; and in portions which are sloping we take only the 

 perpendicular height. Thus, if we suppose the subjoined figure to 



represent the section of a system of pipes, a being the boiler, b the 

 " flow," and m the " return," then we intend the water to ascend in 

 the portions a, b, d, h, and m, and to descend in / and k. Now if we 

 suppose the height of each of these portions to be that set against it in 

 the following table (the height of the slope d being reckoned only as 

 the perpendicular dotted line d') f and if we calculate from the length 

 of the level portions that the water will gradually cool down to the 

 mean temperature set against each, then by multiplying the mean 

 temperature by its corresponding height, we get the relative weight 

 stated in the fourth column. 



