1876.] 



the Theory of Ventilation, 



3 



152 cases gave a recorded sensation helow the theoretical value — that 

 is, the air seemed purer than would have been expected from its 00^. 

 In those cases the average temperature was above, but the average 

 humidity below the mean of Class 1. 



120 cases gave a recorded sensation that exactly corresponded with 

 the theoretical value. In those cases the average temperature was above 

 and the average humidity below the mean of Class 1. 



Arranging these results and putting ~E for the temperature in degrees 

 of Fahrenheit, and H for the humidity per cent., we have 



o r Aggregate difference of the 



+ 58-6r+86H= + 197-70 [1] \ recorded and the theore- 



[ tical value of sensation. 



+ 230-8 E-82 H = - 117-37 [2] Do. 

 + 244-0 r-91 H = [3] Do. 



Adding the two last equations, we have, 



+ 474°-8 E-173 H = - 117-37 [4] Do. 

 From [1] and [4] we can determine the respective values of E and H, 

 which are as follow : — 



E = 0-4730 H = 1-9765 



Or, stated in terms of CO^, by multiplying by 0-1943, 



P = 0-0919 H = 0-3833 per 1000 vols. 



Taking F as unity, we have, 



F : H : : 1-0000 : 4-1789 



Or an increase of 1 per cent, of humidity has as much influence on 

 the condition of an air-space (as judged of by the sense of smell) as a 

 rise of 4°-18 of temperature in Fahrenheit's scale, equal to 2° -32 Centi- 

 grade, or 1°*86 Eeaumur. 



This may be taken as a proof of the powerful influence exercised by 

 a damp atmosphere, corroborating the conclusions arrived at by ordinary 

 experience ; and it follows that as much care ought to be taken to ensure 

 proper hygrometric conditions as to maintain a sufficiently high tem- 

 perature. This is especially the case in the wards or chambers of the 

 sick, in which regular observations with the wet and dry-bulb thermome- 

 ters ought to be made ; these would probably give a valuable indication 

 of the condition of the ventilation, either along with or in the absence of 

 other more detailed investigations. Thus a room at the temperature of 

 60° F. and with 88 per cent, of humidity contains 5-1 grains of vapour 

 per cubic foot : suppose the external air to be at 50° F. with the same 

 humidity, 88 per cent. ; this would give 3-6 grains of vapour per cubic 

 foot ; to reduce the humidity in the room to 73 per cent., or 4-2 grains 

 per cubic foot, we must add the following amount of external air, 



5-1 - 4-2 _ 



4.2-3-6-^^' 



e2 



