in space is to throw something away, or, in other words, lose
mass in order to gain speed by reaction. Which is simply a statement
that as far as we can tell a force can only be exerted relative to two
points--or between two points or masses.

"But this does not account for the continuance of motion once started.

"Inertia says a body will move once started, but it doesn't say why or
how. How does that particle once started gain the knowledge to
continue without some direct control over its spatial framework? That
it will continue, we know. That in the presence of a gravitic field or
a magnetic field or other attractive force at right angles to its
motion, we can create an acceleration which will maintain it in an
exactly circular path called an orbit. But how does it remember, as
soon as that field ceases to exist, where it was going before it was
last influenced? That it will continue in a straight line
indefinitely, without such an influence, we know. That it can be
influenced over a distance by various field effects, we also know.
But what is the mechanism of influence whereby it influences itself to
continue in a straight line? And what handle did we get hold of to
convert that influence of self to our own advantage in moving this
ship?"

* * * * *

Mike stared at Ishie with vast respect.

"I thought you physics boys did it all with math," he said softly,
"and here you've outlined the facts of space that an Indian can feel
in his bones--and you've done it in good, solid English that makes
some sense.

"In other words," Mike was almost talking to himself as he tried to
reword Ishie's theorizing into his own type of thinking, "the particle
in motion creates a strain in the fabric--the field--of space; and
that fabric must attempt to relieve itself of the strain. A particle
in motion makes it possible for the fabric of space to smooth itself
out behind the particle; and the fabric attempts to smooth itself on
through the area occupied by the particle while it is moving, and so
the fabric of space smoothing itself is a constant thrust behind the
particle's motion, continuing that motion and making the particle scat
to where he wasn't going.

"When that same particle is stopped," Mike was visualizing the process
to himself, "the force of the attempt to smooth itself out by the
fabric of space exists equally around the particle on all sides; so
that the particle will be held stoppe