II' 'ARMING OF GLASS-HOUSES. 



79 



the generation of the heat and to pass the heat to hot water, by which 

 it may be carried to any place and in any direction we please. 



In all systems for the circulation of warm water a boiler is 

 necessary. The principle upon which this should be constructed is 

 to afford so large a surface of metal to the fire that all the heat 

 generated should be transferred to the water. It is also desirable 

 that the capacity of the fireplace should be so large as to hold 

 enough fire for twelve hours' consumption. All horticultural boilers 

 should be of the simplest construction. For moderate heating power 

 a simple circular boiler has answered very well with us. Where a 

 larger boiler is required, we have found the saddle-boiler (fig. 93) 



FIG. g 3 . 



FIG. 94. 



FIG. 95. 



unexceptionable ; and had I a large range of buildings to warm, I 

 should certainly have recourse to the Cornish boiler in preference to 

 any other. There are innumerable forms of tubular boilers, and 

 amongst them some complex boilers which some of the first horticul- 

 turists condemn, and which certainly I should never myself use where 

 a choice existed. 



In all cases the water enters the bottom of the boiler by a pipe. 

 The water becomes heated, expands, rises to the top, and flows by 

 a second pipe from the top of the boiler (fig. 94). At my garden the 

 heated water is used in two methods, by one causing it to flow in hot- 

 water pipes in the ordinary way, and by the second (fig. 9$) connecting 



