Human Physiology. 



and tainted with impurities, but it also becomes heated and 

 rises, while there is pouring down into the great parks, squares, 

 broad streets, and all open places cataracts of fresh air out of 

 the sky great downward currents, which then spread out and 

 take the place of the impure air of the upward currents. The 

 air in the centre of Hyde Park, on a still day, differs but little 

 from that of the country. Every open square is a fountain of 

 health. Above the Thames is a great river of pure air flowing 

 up all the streets and alleys on either side. The principle of 

 ventilation is very simple it is to provide a constant and full 

 supply of pure air for every person. But when some hundreds 

 or thousands of persons are crowded into one room, there are 

 practical difficulties. The vitiated air, which naturally rises 

 toward the ceiling, must be allowed to pass out, and for this 

 there is required only a sufficient opening in or near the roof. 

 But fresh air must come in to fill its place; and during the 

 greater part of the year such air, if admitted in heavy draughts, 

 produces chill, discomfort, and disease. There are two reme- 

 dies one to warm the air in a large lower apartment by proper 

 furnaces, before it is admitted into the room in which it is to 

 be breathed; the other to adrrit the fresh air by a great number 

 of small openings. 



Whatever means are employed to ventilate public edifices, 

 schools, railway carriages, cabins of steamboats, most of which 

 are now almost or entirely deficient in proper ventilation, 

 nothing can be safely left to the choice or will of the persons 

 most concerned. People would not breathe at all if it depended 

 upon their volition. The bad air should flow out of, and fresh 

 air into, every place in which people are to breathe, without 

 their having any care or thought about it ; and the first care of 

 an architect should be to adapt every room to its most impor- 

 tant requirement, the health of its occupants. As it is, we are 

 stifled and poisoned wherever we go. Ten persons in a rail- 

 way carriage, are at the mercy of those who sit next the 



