HOT WATER. 



307 



The pits must have a water-tight paved bottom, with a de- 

 clivity of one inch in ten feet. The sides and covers of the 

 channels are loosely jointed, and are permeable by the 

 steam. Stop-cocks are attached to the* pipes, so that the 

 supply of vapor can be adjusted. < Another mode of adapt- 

 ing steam to the production of bottom heat may be seen 

 in Mr. Macmurtrie's Pine-Pit, to be afterwards described. 



Hot Water. More recently the circulation of hot water 

 in iron pipes or vessels has been successfully employed in 

 producing artificial warmth. The temperature derived 

 from this source has all the properties of steam-heat, with 

 the following additional advantages : it is more steady, be- 

 ing less affected by changes of temperature in the open air 

 than in houses heated by fire-flues, or even by steam-pipes ; 

 it is not liable to interruption by the bursting of vessels, 

 and it is more lasting, as water does not cool so rapidly as 

 aqueous vapor. 



The following explanation of the principle of the hot- 

 water apparatus is given by the late Mr. Tredgold, in an 

 excellent paper in the Lond. Hort. Trans., vol. vii. " We 

 may select the simple case of two vessels placed on a hori- 



Fig. 28. 



zontal plane, with two pipes to connect them ; the vessels 

 being open at top, and the one pipe connecting the lower 



