VENTILATION, AND THE REASONS FOR IT. 359 



As the demand becomes less, the difference diminishes. If ozone were 

 taken into consideration, the difference would probably be much 

 greater ; but I do not know what allowance to make for that body, 

 and leave it out of consideration. In the smoky towns there is none 

 at all. 



The conclusion has been drawn by some scientific men that in all 

 spaces, and under every circumstance, the same amount of air must be 

 supplied. Now, it is true that the same amount is to be actually 

 breathed, and, if tbis breath is thoroughly mixed with all the air of the 

 room, the same amount must be supplied for ventilation, whatever the 

 size of the room. But let us suppose the most common case that the 

 thorough mixing does not take place, and we have at once a different 

 amount of air required. 



As to the imperfect mixing, it is so various and characteristic that 

 we cannot reduce it to rules ; we may hold a smoking substance in the 

 midst of an apartment, and find the smoke go directly to an opening 

 without mixing with the air of the room. It goes, too, with a velocity 

 greater than that of the air of the room, otherwise an opening must be 

 supposed sufficient to change the whole air of the room in a few sec- 

 onds, that being the time required for the smoke to reach the opening. 

 If we could drive the impure air in a similar way in a narrow current 

 toward its exit, we might manage ventilation with a very small 

 amount of air. To do this is a matter of great importance, because 

 the expense of building is becoming so great, that very few men can 

 afford to pay for a large enough house, and, while rents are rising, the 

 rooms of the middle classes have actually diminished in some places, 

 and within these few years. Yet the evil of small rooms is great, be- 

 cause rapid currents are required for ventilation ; cold currents are 

 hurtful, and the warm difficult to obtain. If, however, we could ob- 

 tain warm-air currents, it would not be important for us to have the 

 rooms so large. It is a question of price. I believe the warmth must 

 be obtained as the first demand of Nature, and without it civilization 

 will go back. When men are cold, they give themselves to physical 

 exercise, and, if that is impossible, to discomfort, in which the mind 

 refuses to do more than to complain, if it cannot forget. Which is 

 cheapest for us ? Is it to build large rooms and to have less warmth 

 with slow currents, or to build small rooms and to have more warmth 

 with rapid currents ? It is to be wished that the former should be 

 the rule for private houses ; more comfort and convenience are prom- 

 ised, and mechanism is not required ; if it were, it could not be ob- 

 tained. For hospitals, the use of mechanism is more within possibility. 

 The expense of large rooms, when the architecture is of a kind in- 

 tended to ornament a capital city, is very great. Should we not gain 

 by a judicious system of warming ? Our methods of warming are 

 very cumbrous, and we seem to be behind ancient Rome and modern 

 Russia. We warm the air which changes in a moment when a door 



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