--Illustration.
The Travels of the Sun.
FARCOT'S IMPROVED WOOLF COMPOUND ENGINE.
In a preceding article, we have described a ventilator which is in use
at the Decazeville coal mines, and which is capable of furnishing, per
second, 20 cubic meters of air whose pressure must be able to vary
between 30 and 80 millimeters.
In order to actuate such an apparatus, it was necessary to have a
motor that was possessed of great elasticity, and that nevertheless
presented no complications incompatible with the application that was
to be made of it.
In the ventilation of mines it has been demonstrated that the
theoretic power in kilogrammes necessary to displace a certain number
of cubic meters of air, at a pressure expressed in millimeters of
water, is obtained by multiplying one number by the other. Applying
this rule to the case of 20 cubic meters under a hydrostatic pressure
of 30 millimeters, we find:
20 x 30 = 600 kilogrammeters.
In the case of a pressure of 80 millimeters, we have:
20 x 80 = 1,600 kilogrammeters.
If we admit a product of 50 per cent., we shall have in the two cases,
for the power actually necessary:
600
---- = 1,200 kilogrammeters, or 16 H.P.
0.05
1,600
----- = 3,200 kilogrammeters, or 43 H.P.
0.05
Such are the limits within which the power of the motor should be able
to vary.
After successively examining all the different systems of engines now
in existence, and finding none which, in a plain form, was capable of
fulfilling the conditions imposed, Mr.
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