202 



BOOK VI 



A PROJECTING MOUTH OF CONDUIT. B- PLANKS FIXED TO THE MOUTH OF THE CONDUIT 



WHICH DOES NOT PROJECT. 



feet high and three feet in diameter, bound with wooden hoops ; it has a 

 square blow-hole always open, which catches the breezes and guides them 

 down either by a pipe into a conduit or by many pipes into the shaft. To 

 the top of the upper pipe is attached a circular table as thick as 

 the bottom of the barrel, but of a little less diameter, so that the barrel may be 

 turned around on it ; the pipe projects out of the table and is fixed in a 

 round opening in the centre of the bottom of the barrel. To the end of the 

 pipe a perpendicular axle is fixed which runs through the centre of the barrel 

 into a hole in the cover, in which it is fastened, in the same way as at the 

 bottom. Around this fixed axle and the table on the pipe, the movable 

 barrel is easily turned by a zephyr, or much more by a wind, which govern 

 the wing on it. This wing is made of thin boards and fixed to the upper 

 part of the barrel on the side furthest away from the blow-hole ; this, as I 

 have said, is square and always open. The wind, from whatever quarter of 



