OF ARTS AND SCIENCES. 



315 



placed over that produced by a simple cone nearly in the ratio of 10 

 to 13, This is one of the most efficient fixed ventilators with a cap 

 which have been examined by the Committee. The form described 

 in the preceding paragraph, with Cisal pin's plate placed at a certain 

 height above it, is to be ranked in efficiency with that last described. 



"9. The velocity of the current produced in a pipe, the mouth of 

 which is presented fairly to the blast, is nearly constant, whether the 

 mouth be cylindrical, conical, with its larger base towards the blast, 

 or the reverse. The diminished area exposed to the blast, in the latter 

 case, is counterbalanced by the increased velocity consequent upon 

 diminished atmospheric pressure within the cone. 



" 10. A difference of temperature between the impinging blast and 

 the produced current does not, within the limits observed, influence 

 the velocity of the latter. , 



li 



Experiments. 



" In the experiments, each ventilator, when examined, is placed upon 

 a perpendicular fixed tube of tinned iron, in the centre of the mouth 

 of the trunk of the blowing machine. This and all other tubes, when 

 not otherwise mentioned, are 1.25 inches in diameter. The velocity 

 of the blast is 10.36 feet per second, or, as indicated by the revolutions 

 of the handle of the blowing-machine, one revolution per second. 

 The time required for the chlorine to act upon the starch, from the 

 moment it is introduced into the pipe, is given in seconds ; the velocity 

 of the current is given in feet and decimals. The direction of the 

 blast is indicated by the S> > . 



Fig. 1. 



Fig. 2. 



" Exp. 2. Straight tube, cut off 

 obliquely at an angle of 45° ; opening 

 turned from the blast, 



40.0 1.325 



Fis. 3. 



" Exp. 3. Elbow ; horizontal por- 

 tion one inch long, opening turned 

 from the blast, .... 



72.0 0.736 



