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 × 30 = 600 kilogrammeters.

In the case of a pressure of 80 millimeters, we have:

20 × 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.