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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; ©, 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. 
Bul. 70.) 
