Plate X. — Showing vertical sub-earth duct. A, brick chamber 25 to 30 feet below 

 surface and 40 inches inside diameter; B, tile or conductor pipe of galvanized 

 iron; C, main shaft of funnel; D, brick chamber at upper end of duct. The 

 circle and section represent a cast-iron plate to cover brick chamber A, and 

 can be had of King & Walker, Madison, Wis. (From Wis. Agr. Exp. Sta. 

 Bui. 70.) 



