give you any more trouble from earthquake and volcano, but how about other
natural phenomena, the tempest and cyclone for example?"

"Well," replied Thorwald, "we have a theory that time, the great healer,
has cured these evils also. Let me ask, Doctor, if the earth ever receives
any accretions of matter from outside its own atmosphere?"

"Yes, we have the fall of meteorites, foreign substances which we believe
the earth encounters in its path around the sun."

"I supposed such must be the case," Thorwald continued. "And now, when you
consider the great age of Mars, perhaps you will not be surprised to learn
that this new matter, coming to us from the outside, was sufficient to
increase the weight of our globe and gradually decrease the rate of speed
at which we were traveling through space."

"I am surprised, though," said the doctor, "because the accumulation of
meteorolites on the surface of the earth is so exceedingly slow that it
would take millions of years, at the present rate, to increase its
diameter one inch."

"But perhaps they came much faster in past ages. Let me ask you, Doctor,
if it is not a fact that the rate of revolution of Mars around the sun is
slower than the earth's? I suppose you are far enough advanced in
astronomical science to answer that."

"Yes," replied the doctor, "you are correct. I believe the earth speeds
along at nineteen miles a second, while Mars travels only sixteen miles in
the same time."