IV
Over and above such matters as compression, carburation, oiling, circulation of the water, etc., the trembler-blade and the sparking-plug are the driver's especial cares. Should the regulating screw of the one displace itself by the breadth of a hair, should the two opposed wires of the other be touched by a drop of oil or a trace of oxide, the miraculous horse will die on the spot. And around these are still many organs whereof I dare scarcely permit myself to think. Yonder, concealed in its case, like a furious genie confined in a narrow cell, is the mysterious apparatus for the change of speed; and this, if you give a turn to the lever when you come to the foot of a hill, will produce repeated explosions, urging the piston to movement so frantic, that every vertebra of the creature will tremble and give to the slackening wheels a quadruple force before which each mountain will bend its back, and carry the conqueror humbly to its very crown. Further there is the enigmatic mechanism of the live axle which, dispensing with chains and straps, transmits directly to the two back wheels all the extraordinary power generated in its delirious heart. And still lower, beneath the brake, there rests, in its almost inviolable box, the transcendent secret of the differentiator, which, by means of a recent miracle, permits two wheels of the same dimensions, revolving on the same axle and moved by the same motor, to perform an unequal number of turns!