248 
JOURNAL OF THE PLYMOUTH INSTITUTION. 
no account to communicate directly with the open air. An inner 
door is a necessity. The space between the inner and outer doors 
acting as an air lock diminishes the volume of air exposed on open- 
ing the door, and thus equalizes the temperature. 
As houses become smaller, the difficulties of ventilating them 
properly increase ; the inmates then come in contact with the 
exchange currents. Draughts, as is well known, are most prevalent 
in small houses, and are indirectly responsible, year by year, for 
a considerable proportion of the death rate. The evil is not in 
the presence of draughts, meaning thereby simply currents of 
air, but in the proximity of different temperatures acting simul- 
taneously, or almost so, on the body when not prepared for 
these surroundings. Hence it will always be advantageous to 
make an opening for the supply of air, if that supply be drawn 
from a partially erpialized temperature. It would be an error to 
insist on such opening discharging air of a very different tem- 
perature from that of the room. 
Of equal importance in theory, and much more in practice, is the 
introduction of an opening to carry off foul air with the products 
of combustion. No plan could be more objectionable than the 
present, where rooms are hermetically sealed over the ceiling and 
half way down the walls. 
In designing houses, halls, lobbies, and spaces other than rooms, 
ought to be looked on as intermediate heating chambers for the air 
in its route from the exterior to the rooms. A hall, then, ought 
always to have sufficient permanent ventilation to supply the house 
at ordinary times with fresh air. In this way the rooms are supplied 
from a reservoir nearer their own temperature than the external air. 
This plan will be found to answer for very warm as well as very 
cold weather. In all houses of any size ventilation flues ought to 
be made leading from openings in each room to the external air, 
and discharging at an elevated point. 
When it is remembered that in this country rain as a rule 
comes in moderate quantities, and at moderate intervals, the 
influence of the top soil must be admitted to be great, especially in 
the drier parts of the year. The fineness of this top soil retarding 
filtration re-exposes the water to evaporation. This is also true for 
all plants; thus the more vegetable life there is in a district, the 
greater quantity of water will he returned to the atmosphere. 
Not only does a much less quantity of moisture, as river water, 
