38 



The foregoing table shows the discharge, through 

 a ventilator of any height, and for any difference of 

 temperature. Thus, suppose the height of the ven- 

 tilator from the floor of the room to the extreme 

 point of discharge to be thirty feet, and the difference 

 between the temperature of the room and of the ex- 

 ternal air to be 15 degs., then the discharge through 

 a ventilator one foot square will be 347 cubic feet per 

 minute. If the height be forty feet, and the differ- 

 ence of temperature 20 degs., then the discharge will 

 be 465 cubic feet per minute. 



The best form of a ventilator would be a zinc tube 

 about 9 inches in diameter, placed along withinsicle at 

 the highest point of the house, with openings beneath, 

 and the tube elongated and continued up within the 

 chimney of the fire heating the stove, or any other 

 chimney in its vicinity, as in the following sketch. 



The law which regulates the operation of such a 

 tube is this : When equal bulks of two fluids are put 

 into the opposite limbs of a syphon, the lighter fluid 

 is forced upwards with a velocity equal to the velocity 

 which a solid body would acquire in falling, by its 

 own gravity, through a space equal to the additional 

 height which the lighter body would occupy in the 

 syphon, supposing a similar weight of each fluid had 

 been used. This velocity is easily calculated : a gravi- 

 tating body falls 1 6 feet in the first second of time of 

 its descent: 64 feet in two seconds, and so on, the 



