It removes a greater quantity of foul air in a given time and makes the
ventilation more uniformly successful under all conditions.
The James Ventilator is also designed so that it offers little hindrance to
the outflow of air, the air current having to make but one turn and that of large
radius much less than a right angle (see "GG" "HH," Fig. 2).
Actual tests by a competent engineer have shown that the James Ventilator
gives 65 per cent better ventilation than the usual wooden cupola and 30 per
cent better ventilation than the ordinary ventilator for dairy barns now on
the market.
The great superiority of the James Ventilator is due to these two James
principles : ( 1 ) construction that offers the least possible hindrance to the
outward flow of foul air, and (2) the application of suction at the proper point
to help pull the foul air out.
How these two important principles are combined with the best features
of other types of ventilators, at the same time avoiding their disadvantages,
can perhaps best be shown by a brief discussion of the principles on which
ventilators are constructed, and the reasons why certain features are essential.
A ventilating flue is much like a chimney. But while the same principles
apply to both, with a ventilating flue it is necessary to go a step or two further.
A ventilating flue, like a chimney, should be as straight as practicable,
higher than the building and of ample size. Both must be airtight in order to
"draw well. ,,

The ventilating flue, however, cannot be left without a cap, as may oft-
times be done with a chimney, and a little thought will make the reason clear.
