THE HEATIXa AND VENTILATING OF HOTHOUSES. 
327 
the return water arriving at the mid-way point sooner than the return 
from the further off house. If the furthest off houses, on the other hand, 
w^ere on a very much higher level, the tendency would be for the hot 
Avater to rush past the middle houses and the other circulations, and 
possibly the furthest off houses would have to be checked. In short, 
nothing but a careful study of the conditions and regulation of the valves 
will be effective in such a case in getting the required heating where wanted. 
In houses where a high temperature is kept up, especially where the 
sides are pretty high, a 2 or 3 in. pipe round the eaves is very useful to 
prevent down draughts. This has been adopted with very beneficial 
results by Professor Bayley Balfour in the Eoyal Botanic Gardens, 
Edinburgh. 
I have left myself no time to say much about the ventilation of hot- 
houses, but this is less to be regretted because ventilation is a very 
simple matter. In all cases there must be bottom ventilation and top 
ventilation. The bottom openings should be as near the floor level as 
may be practicable, and with orchid-houses and where other delicate 
plants are grown the cold air should be made to impinge on the hot- 
water pipes so that the chill may be taken off. The particular manner of 
doing this must be left for each case to be treated on its merits, the most 
important matter being that the opening arrangement should be such 
that 1 in. or 1 ft. of an opening may be had at pleasure. The top 
ventilation should be at the highest point, and also must be arranged 
so that a very little space may be open in cold weather and as much as 
possible in very warm weather. 
