376 THE GARDENER. [Aug. 



"the practice of sinking the boiler below the level of both the flow and return 

 pipes." For my own part, I began and ended my former letter by a reference to 

 what I consider a necessary evil — viz., a deep stoke-hole. But no one is yet any 

 the wiser for all the information Mr Hammond has vouchsafed us. 



I ask Mr Hammond, as a special favour, to go into the matter in reference to 

 arrangements of houses as above, which, I assure him, from a pretty extensive 

 knowledge of hothouses, is the main difficulty. I am perfectly well aware that 

 various ingenious expedients have been recommended to overcome dips by throw- 

 ing all the hot water up into a box and other means ; but all who are conver- 

 sant with the matter know that the success, where adopted, has not been by any 

 means of such a nature as to lead others to follow ; and if Mr H. has nothing 

 better to recommend, he is again only bringing forward the ghost of bygone 

 days. 



If Mr Hammond's sole object is to prove that after the pipes travel, say 50 or 

 60 feet below the pathway with a gradual rise, they should — or rather the flow- 

 pipe should — immediately on entering the house, rise to its highest point, then 

 gradually slope back to the return, is the best way to lay pipes, I do not know 

 if there is really much necessity for discussion about it. For my own part, I 

 consider it of not the slightest importance, any further than may be desirable 

 from accidental circumstances. If the height is the same, there is no difference be- 

 tween the power necessary to raise the water in a vertical pipe than in a pipe at an 

 angle, whatever that angle may be, from the well-known law of liquids that pres- 

 sure is to be counted by height only ; for "the pressure exerted by a liquid in 

 virtue of its weight (or gravity) on any portion of the liquid, or on the sides of 

 the vessel in which it is contained, depends on the depth and density of the liquid, 

 but is independent of the shape of the vessel and of the quantity of the liquid " 

 — Ganot's Physics, p. 79, — italics are mine. This proves that the expenditure 

 of power is the same in raising water by pressure in a vertical direction as at an 

 angle. It also further proves what I proved already, that the pressure depends 

 on the depth or height and the density of the liquid, so that it makes no differ- 

 ence to the motive power, seeing the friction in both cases must be the same. 



If he objects to Ganot, let him consult any authority he pleases. Chambers, in 

 ' Hydrostatico-Pneumatico,' p. 4, says: "When a pressure is exerted on any 

 part of the surface of a liquid, that pressure is transmitted undiminished to all 

 parts of the mass and in all directions ;" and on p. 7 : "the pressure of water 

 increases in intensity with the depth without regard to the shape or size of the 

 cavity or vessel containing it ; " and again, p. 8 : " the pressure on the horizon- 

 tal bottom of a vessel is as the area of the bottom and the perpendicular height 

 of the liquid, &c, that without regard to the shape of the vessel." It is surely 

 unnecessary to bring forward further proof. Any one who wishes to pursue the 

 subject further should consult the authorities named, or others— Tyndall, Lard- 

 ner, Todmorton, Dr Golding Bird, — they all agree upon this. Having shown 

 that the motive power in a hot- water apparatus depends directly upon the vertical 

 height, and that it makes no difference to this motive power whether the highest 

 point is near the boiler or at the farthest end, I have only to state, further, that 

 the discussion on the point raised by Mr Hammond is not of yesterday. I find 

 that Mr Hood, in his ' Treatise,' p. 12, thus refers to it : "Some persons have 

 imagined that if the pipes be inclined so as to allow a gradual fall of the water in 

 its return to the boiler, additional power is gained. This at first appears very 

 plausible, particularly with regard to some forms of the apparatus." He then 

 proceeds, by a series of elaborate calculations, to prove this idea to be an error; 

 go that the ghost was laid forty years ago, and the apparition Mr Hammond has 



