26 ANNUAL OF SCIENTIFIC DISCOVERY. 



erring effects of the contact of iron, the rolls are covered with a 

 coating of zinc. He drew on the blackboard the details of the 

 machine, which can prepare a cord of bark per hour, equivalent 

 to a barrel of the tanning concentrated extract. Whether leather 

 can thus be made any quicker, is another question. The great 

 practical value of the machine and process is this, that we can go 

 to the woods and get our tanning extracts by the barrel, instead 

 of carting away loads of bark ; thereby securing great economy 

 of time, labor, and space, and opening an immense field of profit- 

 able industry and commerce in supplying other countries where 

 tanning materials are not indigenous. 



VENTILATING FAN. 



At a meeting of the Massachusetts Institute of Technology, Mr. 

 S. P. Ruggles exhibited and explained a model of the Ventilating 

 Fan cJr Blower, invented by himself, now in practical operation at 

 the Institute, and about to be introduced into the State House. It 

 consists of three floats, of which one remains for a short time sta- 

 tionary, while the other two are moving, each in turn becoming 

 stationary. The object of the stationary fan is to act as a wall to 

 prevent the air going back, and to cause the air brought by the 

 ascending float to pass upward through the box which conducts it 

 to the building. This action of the floats is produced by the shaft 

 which carries them being made in three parts, one within two 

 others, each carrying a float. From the condition of rest the first 

 float begins to move slowly, and gradually increases for a quarter 

 of a revolution, then carries the body of air at uniform speed for 

 half a revolution, and then decreases in speed in the last quarter 

 of revolution to the state of rest. When the first float has com- 

 pleted a half revolution, the second float begins to move, to follow 

 in like manner ; the third float begins to move when the first has 

 completed its revolution, and follows in the same manner as the 

 other two, the action of the three producing a constant and uni- 

 form current. 



This action is produced by an ingenious arrangement of wheels 

 of irregularly oval shape, producing a crank motion. The fan at 

 the Institute is vertical, 10 feet in diameter and 10 feet long ; it 

 makes about 12 revolutions per minute, forcing out 700 to 800 

 cubic feet of air at each revolution; this amount must go for- 

 ward, and none can go back on account of the wall of the 

 stationary float. It requires only about one-sixth the power of 

 ordinary fans of this size to move it. In the great number of 

 rotary aspirators and blowers in use in Europe and in this country, 

 centrifugal action from rapid revolution is depended on. In the 

 apparatus of Mr. Ruggles centrifugal action is not the motive 

 force, but the mass of air is drawn in below and forced or buck- 

 eted up, and delivered to the discharge pipe. 



Fan-blowers have been used in which the temporary stationary 

 condition of a float had been employed, as in the apparatus of Mr. 

 Ruggles ; but these plans made use of only two floats, so that no 

 provision was made against the backward flow of the air. In his 



