i879-] HEATING BY HOT WATER. 423 



water circulates properly through the apparatus, minor difficulties in 

 connection with its erection are easily got over. Now with regard to 

 the second consideration. It becomes important when considered in 

 connection with another statement of Mr Makenzie's. The second 

 consideration * says — "by increasing the quantity" (of piping) "the 

 friction increases r in a greater proportion than the power." The 

 statement referred to is a quotation from Ganot's Physics, and the 

 conclusions that Mr Makenzie draws therefrom, and reads as follows : 

 " The pressure exerted by a liquid in virtue of its weight (or gravity) 

 on any portion of the liquid, or on the sides of the vessel in which it 

 is contained, depends on the depth and density of the liquid, but is 

 independent of the shape of the vessel and of the quantity of the 

 liquid." This quotation, Mr Makenzie says, "proves that the expendi- 

 ture of power is the same in raising water by pressure in a vertical 

 direction as at an angle ; " and that it also proves what he proved 

 already, " that the pressure depends on the depth or height and the 

 density of the liquid, so that it makes no difference to the motive 

 power, seeing the friction in both cases must be the same." Now ac- 

 cording to this consideration the motive power is limited in its action 

 by friction. According to the statement, the same amount of motive 

 power that would cause circulation in apparatus of, say, 500 feet of pip- 

 ing with the highest elevation — say, 5 feet immediately above the point 

 on which the fire acts — would cause as good a circulation in an ap- 

 paratus of, say, 5000 feet of piping having the same elevation at- 

 tained by a slow gradient, but situated 500 feet from the point on 

 which the fire acts. Let it be observed that " the height is the same," 

 and the motive power the same in the two apparatuses here in- 

 dicated. But surely the heated volumes of water will meet with more 

 friction in attaining 5 feet of elevation by travelling up a slow 

 gradient of 500 feet in length, than it would meet with by ascending 

 vertically to the same height. The motive power that is the immediate 

 cause of the water circulating in the hot-water apparatus, and the 

 power that is the cause of water finding its levels by gravitation or 

 pressure, are totally different. The power (heat) which is the immedi- 

 ate cause of circulation in the hot- water apparatus is an imparted 

 power. The power by which water rises to a common level in a pipe 

 or pipes is inherent in the water itself. In the heating apparatus the 

 water receives the power to ascend at one point, while at all other 

 points of the apparatus it is parting with that power, and increasing 

 its power to descend. Hence the heated volumes of water should reach 

 the highest point of the apparatus before they part with any of the 

 power by which they reached that point. Now about " 10 or 100 

 miles " of piping being sufficient to drive the water through the 

 apparatus at a speed only equalled by the electric spark. I have to 

 say that Mr Makenzie must know — unless, like that other engineer, 



