68 



is evident, from the circumstance of the air flowing to an 

 apex, that a great amount of power is wasted in producing 

 the increased velocity with which a column of air equal in 

 volume to the two ingress openings of the fan must pass so 

 contracted an area before it is discharged ; hence it is that 

 the fan, as an air-moving machine, has been considered un- 

 equal to the screw. 



The enclosed space of the coffee- curing house at Eathoon- 

 godde has an area in the cross section of 100 superficial feet, 

 it is 70 feet long, and a pair of fans are placed at one end. 

 Kepeated experiments have shown that, when the fans make 

 100 revolutions per minute, a cloud of smoke travels to them 

 from the centre of the enclosed space (a distance of 35 feet) 

 in precisely 15 seconds, hence we have 100 X 35 = 3500 cubic 

 feet of air discharged in a quarter of a minute, or 14,000 

 cubic feet per minute ; a screw of nearly seven feet in dia- 

 meter would be required to discharge the same amount of 

 air, and the cost of it in England is 84 guineas, whilst 

 the pair of fans made and fitted up at Eathoongodde cost 

 under 9Z. 



In the centre of the enclosed space, with a depth of four 

 feet of coffee in the upper floor, the flame of a caudle is 

 blown to a right angle when the whole power of the fans is 

 put on that floor ; near to the fans it is extinguished, the air 

 moving forward with a uniformly accelerated velocity from 

 the farther end towards the fans, owing to the constant ac- 

 cessions made by the air entering the enclosed space through- 

 out its whole length. 



It has already been mentioned that the only entrance of 

 air into the air-chamber beneath the ground-floor is by the 

 opening in which the stove is placed, consequently, when 

 this opening is closed by a damper, it is obvious that the 

 whole power of the fans is exerted on the mass of coffee 

 which is being cured on the upper floor, and that the divi- 



