If the float, through premature or unskilful starting, should get headed downstream, there would be no hope of counteracting its impetus.
Lifting his machine, he lowered it carefully into the opening left by the torn-off plank, until the pedals rested upon the planks on either side and the power wheel was partially submerged.

So far, so good.
In less than a minute now he would either succeed or fail.

It was necessary first to alter the position of the float slightly so that the opening left by the plank pointed across and slightly upstream.

He had often noticed how the pilot of a ferryboat directs his craft above or below the point of landing to counteract the rising or ebbing tide, and this was his intention now; but to neutralize the force of the water with another force not subject to direction or adjustment involved a rather nice calculation.
Very cautiously he waded out upon the precipitous, submerged bank and brought the float into position.

This done, he acted with lightning rapidity.