314 PROCEEDINGS OP THE AMERICAN ACADEMY 



locities of the currents are unequal, the greater velocity diminishes the 

 less, destroys it, or inverts it, according to the excess of velocity. The 

 knowledge of this fact leads at once to the interposition of a plate, to 

 prevent loss of velocity in interfering currents. 



" 5. A thin plate placed upon the extremity of a tube, at the proper 

 angle, causes the impinging current to assume a certain direction, and 

 to produce a certain velocity in the tube ; a similar plate parallel to 

 and above this plate does not increase that velocity. 



" A cone placed upon the extremity of a tube produces similar 

 changes of direction in the impinging current, and similar movements 

 in the tube, but another cone above the first does not increase the 

 velocity of those movements. 



" 6. Beyond certain narrow limits, the velocity produced in a tube 

 by the action of a current on its conical extremity is not increased by 

 increasing the height or diameter of that cone. The full effect of a 

 cone may be obtained when its lower base is not larger than one half, 

 nor less than one third, the diameter of the flue on which it is placed. 



" 7. If a flat truncated cone be fitted to the extremity of a tube, 

 and exposed to the impinging current, a velocity may be produced in 

 the tube of 1.71 feet per second ; if a similar but much smaller hollow 

 truncated cone be inverted and closely secured to the mouth of the 

 first, the velocity in the same tube may by this means be increased to 

 2.21 feet per second. The same increase of velocity will be produced 

 if the internal cylindrical bore of the first cone be made conical, with 

 its larger base upward. By the addition of this secondary cone, or by 

 the modification of the interior of the first cone, the velocity of the 

 current is increased over that produced by the simple cone nearly in 

 the ratio of 10 to 13, and as the effect is as the square of the velocity, 

 its efficiency is increased nearly in the ratio of 10 to 17. This is 

 the best form of the simple fixed cone, and the most efficient fixed 

 ventilator, which has been examined by the Committee. Venturi has 

 shown, that, when a conical tube is applied to a cylindrical pipe, the 

 larger base of this conical tube being 1.8 the diameter of the pipe, 

 and its height 9 times the diameter of this same pipe, the expenditure 

 will, with water, be greater for the cone than for the cylindrical pipe, 

 in the proportion of 24 to 12.1. 



" 8. A hollow truncated cone, with its larger base closed by a flat 

 plate, inverted and placed above a cone similar to that last described, 

 will increase the velocity of the current in the pipe upon which it is 



