of Stoves and oilier Horticultural Erections. 487 



heating more rapidly, and cooling more slowly, than steam ; Gthly, the supe- 

 riority of the egg-shaped boiler. 



" Directions to prevent disappointment in the use of the hot-water apparatus, 

 by preventing, first, the accumulation of air in the angles of the pipe, by taking 

 care that the water in the boiler and the supply cistern shall not sink beneath 

 the level of the top pipes; secondly, by allowing space for the expansion of the 

 metal in the various places when the pipes have to pass through solid bodies 

 of brick, stone, &c. 



" Directions respecting the proper caliber of the conducting pipes, and of the 

 boiler, warning against suffering the accumulation of calcareous or other 

 deposits in the pipes, by he use of unclean water, with an analysis of five 

 different kinds of water (kindly favoured by Mr. Budd, the chemist, for this 

 publication ; see Appendix) ; caution against over-confidence in this changeable 

 climate, and against employing improper persons, i. e. non-practical men, to 

 give designs for houses, &c. Necessary care should be taken to have a proper 

 sized furnace door, and of the pipes when ascending and descending under 

 doorways, &c. ; the effect of arid air being detrimental, of humid air bene- 

 ficial, to the health of plants ; noxious gases evolved from heated air and steam, 

 nutritious gases evolved from hot water, &c. 



" Knowing that both gentlemen and gardeners are hourly subjected to much 

 inconvenience from the bad situation and construction of their green-houses 

 and other horticultural buildings, as well as from the various modes of heating 

 such erections, in consequence of no practical directions having been published 

 for their assistance or guidance by men practically acquainted with the subject, 

 and who, like Hercules, have actually put their shoulders to the wheel, 1 am 

 induced, from having devoted several years to the subject now under con- 

 sideration during my practice in Her Majesty's Botanic Garden at Kew, and 

 in several other departments of the Royal Gardens, as well as in many private 

 establishments, where fruits and plants have been extensively and successfully 

 cultivated, to offer for the assistance and consideration of all persons interested, 

 a few practical remarks after the result of fifteen years' observation and cal- 

 culation, all of which have been gleaned by dint of personal labour, during 

 which time, I regret to say that I have not only witnessed the destruction of 

 fine crops of grapes, and other forced fruits, from badly designed houses, but 

 also from the escape of smoke, pf carbonated, hydrogen, and other destructive 

 gases which are evolved from common flues when over-heated ; a circumstance 

 that must always occur on cold nights in forcing, and in other glass-roofed 

 houses where a large cooling or radiating surface, such as glass, is exposed to 

 the action of the external atmosphere ; the escape of these noxious gases is 

 caused by the unequal expansion and contraction of the materials used in their 

 construction, which leaves apertures between the joints of the bricks, and 

 other parts of the flue. Moreover, it is a fact too well known to gardeners to 

 require comment, that brick flues, after having been in use for a few years, 

 become very unsafe for early forcing, when strong fires are applied, from their 

 liability to burst." 



We ask if it is to be expected that a man who could commit 

 himself to print in terms such as the above is likely to have 

 clear and distinct ideas on any subject? Assuredly, if iron is a 

 dangerous material in the construction of hot-houses, Mr. 

 Thompson is not the man to show why it is so. We have no 

 doubt that he has long entertained a prejudice against iron- 

 roofed hot-houses, from having found, as he says, p. 11., "the 

 strength of three men insufficient to force down the sliding lights 

 for the admission of air;" the cause being the "powerful action 

 of the sun's rays in expanding the iron rafters and lights of a large 



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