178 Trajisactions of the Horticultural Society. 



we proceed to Mr. Tredgold's valuable paper, we must be 

 allowed to express our great satisfaction at the removal of 

 the tax on coals. There will be now much less temptation to 

 employ stable-dung as a source of heat in gardening, a pro- 

 cess by which its qualities as a manure are deteriorated, never 

 less than 50, and we should think, on an average of gardens, 

 90 per cent. Every Number of this Magazine, for more 

 than a year past, has proved that all descriptions of forcing, 

 from the cucumber-bed to the pine-stove, including the hot 

 wall, and the hot border, may be as well performed by hot 

 water as by dung ; and better, except in extraordinary cases, 

 than either by smoke-flues, hot air, or steam. 



" Anew method of applying heat to the purposes of forcing and preserv- 

 ing plants in houses having been discovered, which possesses some import- 

 ant advantages compared with the best method before in use ; and the first 

 instance of its successful application under the direction of Mr. W. Atkin- 

 son, its discoverer, having been published in the Transactions of the Horti- 

 cultural Society (vol. vii. p. 203.), it appeared to me that the principles of 

 the method would form an interesting enquiry, which might not be altogether 

 unworthy of your attention. 



" 1. The power of imitating other climes and other seasons than those 

 which nature affords us, is known and valued as it ought to be; yet it 

 remains difficult even to imagine the extent to which this power may be 

 applied : in this age it produces luxuries of which few can enjoy more 

 than the commonest species ; but in the next — nay, even in our own, 

 there is a reasonable expectation of a considerable addition to the quantity 

 and quality of those artificial productions, as well as to the vast sources of 

 pleasure and information they afford to the admirers and the students of 

 nature. 



" 2. The vehicle employed to convey and distribute heat in the new pro- 

 cess is water ; for it has been found that, in an arrangement of vessels con- 

 nected by pipes, the whole of the water these vessels and pipes contain may 

 be heated by applying heat to one of the vessels ; and that in this manner 

 a great extent of heating surface, and a large body of hot water to supply 

 it, may be distributed so as to maintain an elevated and regular temperature 

 in a house for plants, or indeed in any other place requiring heat. 



" 3. The obvious advantages of this method are, first, the mild and equal 

 temperature it produces ; for the hot surface cannot be hotter than boiling 

 water ; secondly, the power of heating such a body of water as will pre- 

 serve the temperature of the house many hours without attention ; and, 

 thii'dly, the freedom from smoke or other effluvia of smoke-flues. In houses 

 for plants these advantages are most important; and my object is to inves- 

 tigate the principles called into action to produce them, to the end that we 

 may be able to regulate their operation in the various particular cases 

 prising in practice. 



" 4. In order to develope the principles on which a hot-water apparatus 

 acts, we may select the simple case of two vessels placed on a horizontal 

 plane, with two pipes to connect them; the vessels being open at the top, 

 and the one pipe connecting the lower parts of the vessels, and the other 

 theii- upper parts. 



. "If the vessels and pipes be filled with water (^g. 21.), and heat be 

 applied to the vessel a, the effect of heatwUl expand the water in the ves- 

 sel A ; and its surface will, in consequence, rise to a higher level (a «), the 

 former general level surface being b b. The density of the fluid in the vessel 



