63 



a gauge, as the bottom of the bench can be readily seen 

 through the flues, and the presence or absence of standing 

 water noted. 



Overflows should be provided at the back of the bench, 

 so that only a certain depth of water can be added, even 

 by the most careless workman. These can be placed at 

 two inches above the bottom, which experience shows to 

 be about right. 



These items cover the essential features of what is be- 

 lieved to be at present the most perfect system of sub- 

 watering. So far as the application in commercial houses 

 has come to my knowledge, there seems to be misappre- 

 hension of the full philosophy of the system. The soil 

 should at all times be well supplied with air, which 

 largely comes from beneath, and therefore should not be 

 kept too wet. Unless benches are made far deeper than 

 usual, water standing in the bottom of the bench any 

 large part of the time cannot fail to keep the soil too wet, 

 besides depriving it of the circulation of air that should 

 take place through the brick. It must be remembered 

 that the bricks continue to supply water to the soil above 

 long after it has entirely disappeared from the bottom of 

 the bench. The usual depth of soil is scarcely enough for 

 this system, even with the most judicious attention. It 

 would be better to have five or six inches of soil above 

 the bricks, and then an inch of the surface soil can al- 

 ways be kept dry to act as a mulch and protection against 

 fungi. 



After a bench is first filled, water should be applied 

 cautiously and time enough given for the slow process of 

 diffusion. It will take from one to three days for the 

 moisture to appear at the surface after water is run into 



