The shouldered chimney would be sufficient to suck in the
quantity of air necessary for a good combustion if we could at will
increase its dimensions in the direction of the diameter or height. But,
on account of the fragile nature of the material of which it consists, as
also because of the arrangement of the lighting apparatus, we are forced
lo give the chimney limited dimensions. The result is an insufficient
draught, and consequently an imperfect combustion. It became a question,
then, of finding a chimney which, with small dimensions, should have great
suctional power. Mr. Bayle has taken advantage of the properties of
convergent-divergent ajutages, and of the discovery of Mr. Romilly that a
current of gas directed into the axis and toward the small base of a
truncated cone, at a definite distance therefrom, has the property of
drawing along with it a quantity of air nearly double that which this same
current could carry along if it were directed toward a cylinder. In
getting up his new chimney, Mr. Bayle has utilized these principles as
follows: Round-burner lamps have, as well known, two currents of air--an
internal current which traverses the small tube that carries the wick, and
an external one which passes under the chimney-holder externally to the
wick.
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