[STARKEY A BARNEs] DEFICIENT HUMIDITY OF THE ATMOSPHERE 211 



tliose in the open. The evaporation from the wet bulb had thus free 

 play and would be practically at its maximum. 



riie relative humidities under these conditions correspond fairly 

 closely with those obtained by exact chemical analysis. It is of course 

 as one would expect that where full play is given to the evaporation the 

 records ought to be nearer the truth than when the wet and àvy bulb 

 instruments are placed in a still atmosphere and the rate of evaporation 

 is interfered with to a large extent. But one can easily see from the 

 last two observations that no figures of correction are possible because 

 the rate of evaporation depending so exactly upon the movement of the 

 air, any interference with the latter would necessarily throw the results 

 a great way lOut from the truth. 



We bring forward these tests in connection with our discussion of 

 deficient humidity because the wet and dry bulb hygrometer is almost 

 the only instrument used for testing the relative humidity by house- 

 holders. Many observers have found the dryness excessive by using this 

 instrument, but it will be seen that the actual state of affairs is proba- 

 bly much worse than has been imagined. 



Methods have been devised for supplying moisture to the air of 

 houses and buildings, but a few figures to show the amount of moisture 

 required to bring the air up to a normal healthy humidity will be found 

 to be somewhat discouraging. T|hus in an ordinary sized dwelling house 

 when due allowance is made for the amount of air required for each per- 

 son per day something like 33 gallons of water must be evaporated daily 

 to keep the air at a relative humidity of 75 per cent. Other difficulties 

 arise when this is accomplished. Kapid condensation takes place on the 

 windows when the air temperature outside is very low. Experience has 

 shown that this commences at a humidity of about 40 per cent. We are 

 inclined to think that much could be accomplished by maintaining the 

 humidit}^ even at this latter figure, and that the question should be 

 earnestly considered in order to improve the general health of the large 

 proportion of people who spend the greater part of their life in artificially 

 heated buildings. 



