About five hundred miles is the limit of a man's ignorance; he then knows enough to make trouble; at the end of another five hundred he is of assistance, at the end of the third he will run the machine himself--your greatest pleasure is in the first five hundred.

With some precocious individuals these figures may be reduced somewhat.
The Professor adjusted his spectacles and looked at the machine: "A very wonderful contrivance, and one that requires some skill to operate.

From lack of experience, I cannot hope to be of much practical assistance at first, but possibly a theoretical knowledge of the laws and principles governing things mechanical may be of service in an emergency.

Since receiving your telegram, I have brushed up a little my knowledge of both kinematics and dynamics, though it is quite apparent that the operation of these machines, accompanied, as it is said, by many restraints and perturbations, falls under the latter branch.

In view of the possibility--remote, I trust--of the machine refusing to go, I have devoted a little time to statics, and therefore feel that I shall be something more than a supercargo." "Well, you _are_ equipped, Professor; no doubt your knowledge will prove useful." "Knowledge is always useful if people in this busy age would only pause to make use of it.