Note 1 — Chapter X

The wall of force known as field X-573 was created at any point the operator wished, by merely setting the controls. The coordinates so selected ruled the placing of the field in space. Thus by placing it at one point, and advancing the controls gradually, it simply moved through space, any force its movement applied, reacting directly on space, not on its source of energy. This apparent "lifting by the bootstraps" seems to defy the third law of motion, but actually the reaction is taken up by space, by the intertwined fields of a million millions suns. Similarly, if the gravitational field was fixed in space, then the ship would fall into it, and changing its coordinates would move it along as did the force-field.