378 THE GARDENER. [Aug. 



friction in such a length of small pipe. It is rather an intricate subject ; but I 

 may mention that, roughly speaking, the friction on water flowing through a 

 halt-inch pipe is relatively eight times as much as through a 4-inch pipe,— so 

 much so that, in a very long, small pipe, friction sometimes, as in J. S. W.'s case, 

 stops the flow altogether. When water lias to circulate through a very long pipe 

 in heating, it is necessary to use steam or other power to force the water, and 

 various ingenious engines have been from time to time adopted for this purpose. 

 If J. S. W. is satisfied that his "boiler of the future" is the boiler of the 

 future, the failure of the gas-pipe need not discourage him. Friction is apt to 

 be forgotten, but it is a most important element, and should not be lost sight of. 

 Where it is not considered, the theory as well as the practice is defective. — 

 Your obedient servant, A. D. Makenzie. 



July 11, 1879. 



When the discussion on this subject was first opened by Mr Hammond, I 

 understood that his object was to show that, in ordinary cases, deep stoke-holes, 

 and giving the "flows a continuous ascent from the top of the boiler to their 

 farthest point of extension in the building or buildings to be heated," were 

 unnecessary. Since various theories have been advanced as to the cause of the 

 water circulating, it now seems to me more of a theoretical quibble than a 

 comparison of attested facts. 



In the July number, R. Inglis alludes to an "old fitter," who boasts of one 

 pipe acting as a flow and return. In that case there would be two currents of 

 water, travelling in opposite directions, the upper stratum going from, and the 

 UDder returning to, the boiler. This is what will occur in the flow when a con- 

 tinuous ascent is given them, not only at the time of " setting the fire agoing," 

 but also while radiation of heat from the pipes continues. This I have proved 

 by inserting a glass cylinder about 2 feet long, the same size as the flow-pipe, 

 so that it forms a part of the same ; and after mixing with the water particles 

 of matter of about the same specific gravity as the water, the two opposite 

 currents were plainly visible. 



R. Inglis "predicts" that a greater quantity of water would flow if the 

 pipes were to ascend instead of descending on leaving the boiler. One of the 

 houses I alluded to in the May number has equal to 350 feet of 4-inch pipe, 

 aud the flow runs down an incline of about 14 inches to where it enters the 

 house ; then it continues its course on a level, and on leaving drops about 13 

 iaches, followed by a slight descent to the boiler, near which is one of Mes- 

 senger's valves. 



The action of this apparatus I will endeavour to describe. Thus, supposing 

 the whole to be cold, and the valve closed : the fire is set agoing, and the 

 water in the boiler is raised to 200° Fahr. If you then examine the boiler, 

 wdiich is uncased for the purpose, you will find that to the touch there is 

 scarcely a perceptible difference in temperature between the bottom and top. 

 The return-pipe, so far as the valve, will be hot. That part of the flow on a 

 level with the aperture where the water leaves the boiler will be hot also, but 

 the part which is below that level cold, as at the commencement. Open the 

 valve. What is the result ? The hot water speedily passes down the flow, and 

 the bottom part of the boiler becomes cold by the inward rush of cold water, 

 and continues cold, however fierce the fire may be, until the whole of the cold 

 water in the pipes has made its circuit and become heated. 



R. Inglis thinks J. H. " will no doubt be done for ever with the old system." 



