Withy. — On Sanitation and Ventilation. 473 



for water, and inner (or warm) air for air, and to remember 

 also that the air which flows into a house is being continually 

 warmed, and caused in its turn to float out, to see that this is 

 the constant operation which gravitation tries to carry on in a 

 house. 



To pass from this illustration, another fact must be borne 

 in mind — viz., that the various openings into a house are con- 

 stantly acted upon by the varying currents of air which are 

 moving outside. The effort of the cool air to get in at 

 some openings from which warm air is trying to escape, 

 coupled with the baffling influence of outside currents, con- 

 stitute the principal difficulties with which we have to deal. 

 These efforts which Nature makes to prevent a stagnation of 

 air in any part of her domain do, within certain limits, venti- 

 late our houses. Why, then, should we not be content with 

 what Nature does ? The answer must be that her efforts are 

 too rough-and-ready, and therefore need regulation in order to 

 adapt them to our requirements. 



Before attempting to regulate them we must decide — firstly, 

 what the nature of our requirements is ; secondly, what is the 

 measure of the necessary modification; and, thirdly, under 

 what restrictions must this modification be carried out. The 

 nature of our requirements is the maintenance of a certain 

 degree of coolness and purity in the air contained in our 

 rooms so that it may suit the purposes of breathing. The 

 measure of the necessary modification of nature's work will be 

 the amount by which it falls short of providing the cool and 

 pure air required in any given instance. The restrictions to 

 be observed are threefold — (1) That from the exits provided 

 for the warm air to escape at no downdraughts must proceed ; 

 (2) that in admitting fresh air no draught must be produced 

 such as may endanger our health or comfort ; and (3) that the 

 air must not be changed so rapidly as to lower the tempera- 

 ture unduly. 



Before suggesting various contrivances for effecting these 

 objects, let me say that, as I am treating only of dwelling- 

 houses of moderate dimensions and not of large buildings for 

 public assemblies, it will be unnecessary to speak of steam- 

 fans, of furnaces, of enclosed gas-jets, or even of water-sprays 

 as agents for the removal of warm air. The original cost and 

 current expense of two at least of these methods entirely pre- 

 vent their use in ordinary dwellings. Of the two others — 

 viz., the enclosed gas-jet and the water-spray — I have no 

 experience, having been inclined to view them too much 

 in the light of an extravagance to make a trial of them. 

 I am therefore left to make the best I can of gravitation 

 and of the wind, two agents which cost nothing, but which 

 may be guided in such a way as to render valuable service 



