212 



THE POPULAR SCIENCE MONTHLY. 



then also the state of the air was anything but desirable. It was only 

 with 2,120 cubic feet that the medical and other authorities fourd 

 themselves satisfied. 



At present the demands for ventilation in France sound very dif- 

 ferent from what they were about twenty years ago. They are now 

 per hour and person : 



Hospitals for ordinary cases 



" wounded 



" epidemics . 



Prisons .... 

 Workshops, ordinary 



" unhealthy 



BarracliS, day 



" night . 

 Theatres .... 



Large rooms for long meetings 



" " shorter " 



Schools for children . 



" adults . 



Such are the changes of times. 



Now the many crevices, holes, and pores in our dwellings will no 

 longer be considered by you as unlimited means of change of the air, 

 since you know how large that change has to be ; you will rather feel 

 anxious whence to procure such enormous quantities when you sit 

 quietly within your four walls where you do not feel the least draught, 

 where no curtain moves, and a feather lies quietly on the floor. This 

 sensation of calm we owe to the insensibility of our nerves and yet 

 the air moves. 



In order to give you some idea of the influences of differences of 

 temperatm-e of more or less well-shutting doors and windows, of a fire 

 in a stove opening into the room, and of the partial opening of a win- 

 dow, I will give you shortly the results I obtained with the aid of the 

 carbonic-acid measurement. The room had brick walls, and its size 

 was 2,650 cubic feet. 



With a difference of temperature of 34 Fahr. (66 in- and 32 out- 

 side), the contents of the room .changed once in one hour, equal to 

 2,650 cubic feet. 



With the same difference, but a good fire in the stove, whose com- 

 munication with the chinmey was made as free as possible, the change 

 of the air rose to 3,320 cubic feet, or about twenty-five per cent. When 

 all openings, crevices in windows and doors, were thoroughly pasted 

 up, there was still a change of 1,060 cubic feet per hour, or a fall of 

 twenty-eight per cent. With a difference of temperature of 71 in- and 

 64 outside, the change amounted to 780 cubic feet only per hour. 

 When opening a window of eight square feet, the change rose to 1,060 

 cubic feet per hour. These quantities are instructive. They show 

 that a difference of temperature of 34 with carefully-shut openings 



