328 THE GARDENER. [July 



possible, and to have the return current with the greatest possible fall, would 

 be the best means to insure a speedy circulation. This view is corroborated by 

 your correspondent "J. H. " in last month's number. And this is also the 

 conclusion, 1 think, Mr Hammond arrives at in disposing of " C. M.'s" theory 

 of the circulation. The idea of hot-water engineers, that a continuous rise in 

 the flow-pipe, no matter of what length, accelerates circulation of the water, 

 may turn out to be, like many another popular idea, a fallacy. 



Robt. Stevens. 



IV. 



The interesting discussion now taking place in ' The Gardener ' on heating 

 by hot water will be the means of showing to a great extent whether deep 

 stokeholes are a necessity or not ; and I am in a position to coincide with Mr 

 Hammond that deep stokeholes in many cases are not required. "We have in 

 use tubular and saddle boilers, with a hermetically sealed box placed nearly 

 above them, and into this box the hot water flows from the boiler, and then 

 falls perpendicularly 7 feet to the pipes, which are then level throughout, the 

 return pipe only falling 1 foot gradually at 9 feet from the boiler. It will 

 thus be seen the only rise in the pipes is immediately above the boiler, and the 

 returns fall at 9 feet from it — one boiler alone heating five houses, comprising 

 an early vinery and stove ; and during the past winter the heating arrange- 

 ments were quite satisfactory. It is well to state that each range of houses is 

 built on a level, and it is only in such cases this system could be satisfactorily 

 carried out. But this system in our case proves conclusively to my mind that 

 a continuous rise and fall is not required to cause circulation of hot water in 

 pipes, and only where houses are built on different levels is it necessary to 

 have the pipes highest at the extreme point, and in such cases the return pipe 

 is high also. The theory that the higher the extreme point of the flow-pipe 

 the more rapid the circulation of water in them, to my thinking is an error ; 

 for however high the elevation, the water would remain stationary without 

 some other agency to bring about circulation, and the main agent is heat, and 

 the more heat that is applied the quicker the flow. To further convey my 

 meaning, let us commence with a fire just lit, and the boiler and pipes filled 

 with cold water — that is, of equal density. The water in the boiler exposed to 

 the heat will gradually get more rarified, and is displaced by the denser body 

 which rushes in and takes its place, which is also made lighter and is again 

 displaced, causing suction along the whole length of piping, drawing the water 

 onwards in its wake, — and shows that however high the piping at the extreme 

 end, the real centre of circulation is in the boiler, and the quicker the water is 

 heated the qiiicker its displacement and the stronger the suction, and, as a con- 

 sequence, the more rapid is the circulation of water in the pipes. I would here 

 point out also that the higher the ascending pipes, the more suction is required 

 by the descent to draw the water from the ascending pipes, and in this way 

 the high elevation is equalised to a proportionate degree. As I have based 

 my argument on suction, and it brought about by displacement of the lighter 

 by a heavier body in the boiler, I may be allowed to show that it is suction 

 that causes the circulation of hot water in pipes, and this can be conveniently 

 exemplified by drawing a portion of the water off, leaving a vacuum at the 

 highest point : the remaining body of water will then find a common level, 

 and circulation in the pipes will cease. This shows that if the fire forced the 

 heated water up the flow-pipe, it would continue to do so until the returning 



