BUILDING THE RANGE 83 



For the roof ventilation it is considered best to have a 

 row on either side of the ridge. It may not be necessary to 

 use both, but in case of a severe wind, the row on the side 

 from the prevailing wind could be raised and severe drafts 

 in the houses avoided. 



Roof ventilators may be continuous or intermittent. 

 Many of the best growers believe that intermittent 

 ventilators are preferable because they equalize the tem- 

 perature better as the air is admitted. The warm air 

 rises from the pipes and strikes the glass of the permanent 

 roof between the ventilators, and as the cold air is admitted, 

 it is warmed by the hot air on three sides of the vents. 

 With continuous ventilation it is all admitted in a con- 

 tinuous line. 



Whether continuous or intermittent systems are used, 

 the ventilators should not be very heavy, for they must 

 be easily and quickly raised without severe jars to the roof 

 and ridge. They are usually not over thirty inches wide, 

 but this varies with the width of the houses. 



There are various types of apparatus used for operat- 

 ing the ventilators. The principal factors of a good ap- 

 paratus are that it must be strong, so that comparatively 

 long areas of ventilators may be raised quickly and easily, 

 and the section of glass at the farthest end of the system 

 must be opened and closed just as readily as the section 

 next to the controlling shaft. The apparatus should be 

 simple and easily adjusted. It should also be of suffi- 

 ciently small dimensions so that it does not prevent the 

 sun's rays from striking the plants. Each section should 

 be carefully adjusted so that all will close tightly at the 

 same time. Self-oiling, closed-geared, ventilating shafts 

 are now used in many large ranges. 



In high houses, when the night watchman cannot see the 



