332 WARMING AND VENTILATION. 



of air an hour to a horse, with a velocity of 28 inches a second, which 

 may be produced by a difference of temperature of 11° to 13° between the 

 external air and that of the stable. This requires that the chimneys 

 have a sectional area of 108 to 124 square inches to a horse. 



By means of this ventilation, the hygrometrical condition of the air in 

 the stable will be maintained within convenient limits. 



144. Use of gas-burners. — The ventilation of stables may be increased 

 by making use of the heat given out by gas-burners used to light them 

 up at night, which then allows of reducing the sectional area of the 

 ventilating-pipes. 



145. Cow-houses. — What precedes relates to work-animals. In the 

 case of milch-cows, it appears that a certain drowsy laziness is favorable 

 to the production of milk ; and in such cases it is necessary to limit the 

 ventilation to what is absolutely necessary for health. 



MEANS OF CONTROL. 



146. Means to be used to determine the condition and the results of a 

 system of ventilation. — It has been shown by the numerous examples 

 that precede that the establishment of a complete and regular renewal 

 of air in occupied places in reality presents no difficulty, and that the 

 rules to be followed are very simple. Their application will be equally 

 so, and will involve but little expense if architects take care to devise 

 j)lans of ventilation at the same time that they make the plans for con- 

 struction, instead of waiting till the buikling is almost finished. 



But when all the arrangements have been made to secure the renewal 

 of air, the first thing to do is to examine whether the desired results 

 have been obtained, and the second is to regulate the operation of the 

 apparatus. 



To determine what are the amounts of air carried off and drawn in, a 

 small portable instrument is used, called an anemometer, consisting of 

 a wind-mill with light and easily-moved vanes, connected with gear- 

 wheels and pointers, which indicate the number of turns made by the 

 vanes in a given time. 



Experiments show that with an apparatus of this kind the velocity 

 of the air may be deduced from the number of turns of the wings by 

 means of an equation of the form : 



V being the velocity in a second ; 



a, a constant term, expressing the velocity of the air at which the in- 

 strument commences to movej 

 &, a constant number ; 

 j^, the number of turns indicated in a second. 



Thus, one of the anemometers of the Conservatory has the formula: 



V (in inches) = 8.GG + 7 N 

 This instrument should be placed, as far as possible, in a part of the 

 flue traversed by the air, where the velocity is uniform and well regu- 



