ctuate and control that gigantic
projector. Immense hour and declination circles could be read by optical
systems from the operators' seats--circles fully forty feet in diameter,
graduated with incredible delicacy and accuracy into decimal fractions
of seconds of arc, and each driven by variable-speed motors through
gear-trains and connections having no backlash whatever.

While Rovol was working upon one of the last instruments to be installed
upon the controlling panel a mellow note sounded throughout the
building, and he immediately ceased his labors and opened the
master-switches of his power plants.

"You have done well, youngster," he congratulated his helper, as he
began to take off his protective covering, "Without your aid I could not
have accomplished nearly this much during one period of labor. The
periods of exercise and of relaxation are at hand--let us return to the
house of Orlon, where we all shall gather to relax and to refresh
ourselves for the labors of tomorrow."

"But it's almost done!" protested Seaton. "Let's finish it up and shoot
a little juice through it, just to try it out."

"There speaks the rashness and impatience of youth," rejoined the
scientist, calmly removing the younger man's suit and leading him out to
the waiting airboat. "I read in your mind that you are often guilty of
laboring continuously until your brain loses its keen edge. Learn now,
once and for all, that such conduct is worse than foolish--it is
criminal. We have labored the full period. Laboring for more than that
length of time without recuperation results in a loss of power which,
if persisted in, wreaks permanent injury to the mind; and by it you gain
nothing. We have more than ample time to do that which must be done--the
fifth-order projector shall be completed before the warning torpedo
shall have reached the planet of the Fenachrone--therefore over-exertion
is unwarranted. As for testing, know now that only mechanisms built by
bunglers require testing. Properly built machines work properly."

"But I'd have liked to see it work just once, anyway," lamented Seaton
as the small airship tore through the air on its way back to the
observatory.

"You must cultivate calmness, my son, and the art of relaxation. With
those qualities your race can easily double its present span of useful
life. Physical exercise to maintain the bodily tissues at their best,
and mental relaxation following mental toil--these things are th