472 THE GARDENER. [Oct. 



and in other confined places is more awkward, as they fall from the 

 point where they enter the house to the far end, and then continue to 

 fall in the return, thus taking up twice the height compared with pipes 

 that rise to the far end and fall in the return— a fact alone which would 

 often entail great trouble in a long house. It appears to me that Mr 

 Hammond has left out one very important fact in his theory — I say 

 theory, because I find no statement that he has succeeded in heating a 

 range of houses on his plan ; if he has, I shall be only too glad to make 

 the journey north to see the apparatus at work, if he will kindly per- 

 mit me — and that is, air. 



Water, when heated in the boiler, gives off air in greater or less pro- 

 portions ; and that it continues to do so after it leaves the boiler, or that 

 it at least carries the air with it for some distance, is proved by the fact 

 that, in a large apparatus having air-cocks instead of open air-pipes, 

 air is found to accumulate at all the cocks, even those most distant, 

 and not at that only where it would the most easily go in leaving the 

 boiler. Now the retarding of the circulation by friction is so much 

 greater where the water has to pass under confined air than when 

 passing under the upper surface of pipe, that I have known it stopped 

 on one side of a house where there was a slight inequality (often not a 

 quarter of an inch) in the rise of the pipes, which allowed the air to 

 accumulate ; on removing the inequality, the water at once circulated 

 properly. Yet Mr Hammond advocates an arrangement of pipes in 

 which every particle of air which passes beyond the highest point above 

 the boiler has to fight its way back against the flow of the water to 

 that point before it can escape. Has he ever watched the air under 

 the ice covering a stream ? I have ; and the way in which a large 

 bubble, detached by the stream from air accumulated at a high point, 

 was carried down, struggled part of the way back to be carried down 

 again, until it often took it minutes to regain its place, taught me that 

 it could not be wise to expend the force of the flow of hot water in 

 contending with the inclination of air to reach the highest point. Why 

 not allow the air to go the same way with the water ? He will say, 

 " Why not then let the water rise the whole way until it is about to 

 re-enter the boiler if you are correct 1 " I would, if the houses were 

 built for the pipes, and not the pipes for the houses. Careful experi- 

 ments were made near Derby by a gentleman in heating a large factory 

 where it was possible to arrange the pipes either to rise to the highest 

 point at first or at last ; he tried both, and proved to his satisfaction 

 at least, that the circulation was quicker, and that less coal was re- 

 quired to maintain the same heat in the room, with the latter arrange- 

 ment. 



When the hot water leaves a boiler it must be replaced with other 

 water out of the return-pipe, and the quicker it is replaced the quicker 

 will be the circulation. Does Mr Hammond intend to state that water 

 in the return-pipe will fail to fill the vacuum caused in boiler by the 



