whole length of the furnace,
whereby motion is given to the bars, and the coal is thus carried gradually
forward. It is very doubtful whether any of these contrivances satisfy all
the conditions required in a plan for feeding furnaces of the ordinary form
by self-acting means, but the problem of providing a suitable contrivance,
does not seem difficult of accomplishment, and will no doubt be effected
under adequate temptation.

164. _Q._--Have not many plans been already contrived which consume the
smoke of furnaces very effectually?

_A._--Yes, many plans; and besides those already mentioned there are
Hall's, Coupland's, Godson's, Robinson's, Stevens's, Hazeldine's, Indie's,
Bristow and Attwood's, and a great number of others. One plan, which
promises well, consists in making the flame descend through the fire bars,
and the fire bars are formed of tubes set on an incline and filled with
water, which water will circulate with a rapidity proportionate to the
intensity of the heat. After all, however, the best remedy for smoke
appears to consist in removing from it those portions which form the smoke
before the coal is brought into use. Many valuable products may be got from
the coal by subjecting it to this treatment; and the residuum will be more
valuable than before for the production of steam.

STEAM.

165. _Q._--Have experiments been made to determine the elasticity of steam
at different temperatures?

_A._--Yes; very careful experiments. The following rule expresses the
results obtained by Mr. Southern:--To the given temperature in degrees of
Fahrenheit add 51.3 degrees; from the logarithm of the sum, subtract the
logarithm of 135.767, which is 2.1327940; multiply the remainder by 5.13,
and to the natural number answering to the sum, add the constant
fraction .1, which will give the elastic force in inches of mercury. If the
elastic force be known, and it is wanted to determine the corresponding
temperature, the rule must be modified thus:--From the elastic force, in
inches of mercury, subtract the decimal .1, divide the logarithm of the
remainder by 5.13, and to the quotient add the logarithm 2.1327940; find
the natural number answering to the sum, and subtract therefrom the
constant 51.3; the remainder will be the temperature sought. The French
Academy, and the Franklin Institute, have repeated Mr. Southern's
experiments on a larger scale; the results obtained by them are not widely
different, and are per