so as to intercept the hot gases as completely as possible; and also, of
course, obtain heat by conduction from the sides of the annular body.
It is evident that the number and dimensions of these tubes might be
increased so as to abstract almost all the heat from the escaping fumes,
but for the limitations imposed, first, by a consideration of the actual
quantity of air required to support combustion, and, secondly, by the
obligation to let sufficient ascensional power remain in the gases which
are left to pass out through the upper chimney. If the gases are cooled
too much, they will either fall back into the lamp and extinguish the
flame, or will be removable only by the draught of a long chimney. It
will probably be the aim of the inventor to balance these requirements,
and so to produce burners with very short or longer chimneys, according
as appearance is to be consulted or the highest possible effect
produced. The burner is a ring of brass tubes of considerable diameter,
in proportion to the quantity of gas consumed, and thus provides for
the delivery of gas expanded by heat. In connection with this device
an explanation may be found of the failure of the British Association
Committee on Gas Burners to find any advantage from previously heating
the air and gas consumed. The Committee did not make the necessary
provision for the increased bulk of the combustible and its air supply,
caused by their heightened temperature; and the same quantity of gas
measured cold (at the meter) could only be driven through the ordinary
small burner holes at a velocity destructive of good results. Herr
Frederick Siemens perceived this in his early experiments, and not only
increased the orifices of his burners, but provided for the closer
contact of the more rarefied gas and air by the use of notched
deflectors, which are now an essential part of his apparatus. Mr.
Grimston also uses separate tubes of large area for his hot gas, but
dispenses with deflectors, save in so far as the same duty may be
performed by the plain lower edge of the inner cylinder of the lamp