326 THE GARDENER. [July 



pipes at the highest point of elevation, and before the heavy column in the 

 return would draw up the column in the flow, the air would rush in and fill up 

 its place, which he can prove by a siphon. The only inference he can draw 

 from my statement, that the highest point of the structure will be the hottest, 

 is, "that it suffers no diminution of heat until it reaches that point." It is 

 needless to refer further to such an absurdity. Nevertheless, it is a well- 

 known fact that a house situated above the level of the others is the hottest 

 from its having a quicker circulation, which proves the value of elevation. An 

 imperfect circulation would take place by Mr Hammond's principle of con- 

 struction on a small scale ; but on an extensive system it would result in dis- 

 appointment, where there are pipes branching from the main flow to houses at 

 different points of the apparatus. On his principle there is neither a vertical 

 nor gradient rise from the main flow to the houses to induce the water to 

 circulate, consecpiently the circulation would principally take place in the 

 main flow and return, which are not unfrequently under outside paths. It is 

 unnecessary to advert to the fact that the rapidity with which water circulates 

 is in proportion to the elevation and the difference of the weight of the two columns 

 of water, which has already been ably treated of by ISIr Makenzie last month. 

 I do not wish to enter into a mere conflict of words with Mr Hammond, which, 

 although it may affect to search after truth, in reality only raises such a dust 

 that we are apt to lose sight of the subject. But with a single eye to truth, 

 I have not the least objection. C. M. 



II. 



Mr Hammond has failed, I think, to bring anything forward of material 

 value in support of his views on the circulation of hot water. He seems to 

 have been more anxious to point out that there is no analogy between the 

 emptying of a cistern by meaus of a syphon and the circulation of w r ater in a 

 heating apparatus, than he has been to explain why it is that the quickest cir- 

 culation takes place in the highest parts of the apparatus, in preference to 

 those coils of pipes that are less elevated above the boiler. If Mr Hammond 

 can prove that it is not the additional weight of water in the return-pipes, but 

 something else, that causes this to take place, he will be doing good service by 

 at once correcting the error which has so long been entertained by hot-water 

 engineers. I am quite willing to yield the point as to the ascent. I think I 

 said it was immaterial. I would as soon have a vertical ascent as a slow gra- 

 dient. Mr Hammond's mode of fixing pipes will not be very likely to meet 

 with much favour by either gardeners or hot- water engineers, if it was for no- 

 thing else but for their appearance. Fancy a house, say 60 feet long, with 

 four rows of pipes along the front ! On entering the house the flow-pipes com- 

 mence a descent of, sa} r 1 in 120 — that is, 6 inches in a length of 60 feet. The 

 return-pipe must have the same slow descent at least, so that when the latter 

 reaches the point where the pipes enter the house, there will be a clear space 

 of 12 inches between the flow and return pipes. This I think would not look 

 so well, nor be so convenient in fitting, and moreover would occupy more 

 room, than they would if fitted up on what I suppose we will soon have to call 

 the "old system." I think it would be better to adopt a medium course, that 

 of having the flow and returns both level inside the house, and so parallel to 

 each other. This is done by many, and with as much success as those fitted 

 with a slow ascent. 



