1879.] HEATING BY HOT WATER. 375 



hotter Avater get up this pipe except it force the colder and heavier water before it, 

 for the water at the very top of the boiler must be hotter and lighter than at a point 

 4 feet away ? That a lighter fluid, bulk for bulk, can force a heavier uphill, 

 every mercurial barometer, every pump and chimney in the country proves. All 

 circumstances connected with the case show conclusively that this back current 

 can only exist for a few minutes after the fire is kindled, and is, as Mr Hammond 

 says, not worth talking about. 



To satisfy those of your readers who have taken the trouble to follow this dis- 

 cussion, and whose tastes and habits of thought have not led them to investigate 

 the matter, I may state that in a heating-apparatus I have fitted up for the very 

 purpose of experiments, there is inserted in the flow-pipe, about 4 feet from the 

 boiler, four glass slips 6 inches long, 1| inch broad, one on top, one on bottom, 

 and one on each side. By watching the flow of the water, it can be seen, with- 

 out the shadow of a doubt, that four minutes after the fire is put on, forward 

 motion begins at this glass, and two minutes after it begins the whole body of the 

 water from top to bottom, from side to side, goes forward up the hill from the 

 boiler, and not a vestige of a return current. It is impossible, from the nature 

 of the case, it could be otherwise. This apparatus, I may say, contains about 

 150 feet of 4-inch pipe, and is erected in such a way that it can be made to have 

 a rise to far end 60 feet away from boiler ; or with a continuous run down from 

 top of boiler to return. I may also state, that from elaborate experiments car- 

 ried out by inserting a series of thermometers in the pipe, and noting the rise on 

 the register, I find that, with a rise to far end, and H foot more height, the water 

 goes round several minutes quicker than with a continuous fall, as Mr Hammond 

 recommends. This is again exactly what one would expect— viz., that the cir- 

 culation should be slower with the less height. It makes no difference where 

 the highest point is — not a shade of difference. I may say further, that these 

 trials have been repeated over and over again with the same result ; and should 

 any reader of ' The Gardener ' have any doubts remaining, I shall be delighted to 

 place the apparatus at his disposal, and let him satisfy himself. I can send you 

 figures and full particulars should any one desire to see them. 



Now as to the stoke-hole, which is really the important point in this discus- 

 cussion, I have a difficulty in understanding Mr Hammond's position. What 

 does he propose ? I find in my experience, which has been considerable— having 

 been, speaking roughly, connected with the erection of about six or seven hun- 

 dred ranges of glass, large and small — the great difficulty to be, having to pass 

 doorways and passages, and in ninety-nine out of every hundred cases where we 

 have a deep stoke-hole this is the cause. I am sure every one concerned will 

 be delighted to find some means of avoiding this unmitigated nuisance. "Well, 

 what does Mr Hammond advise ? My firm have several ranges of glass to heat 

 just now with a passage running from end to end of the range about 2 feet from 

 the back wall ; the boiler is to be placed on the north side of the passage, and as 

 the passage has to be crossed at least in three different places, we are at present 

 in the belief that we must sink the boiler until the flow-pipe is at least a few 

 inches below the floor level. We are afraid of water, and may have to cut a 

 drain, at considerable expense, to avoid being drowned out. 



Now if Mr Hammond can make the apparatus work as well with the bottom 

 of the boiler one foot below the floor level, we shall not only be delighted to have 

 the information, but pay him handsomely for it ; or, if he takes out a patent, I 

 will guarantee that he will soon make a large fortune. I confess I am quite at a 

 loss, after reading his three letters, what it is he proposes in this direction. 

 He commenced his original article in the February number by reprobating 



2c 



