on earth are they for?"

"You don't know?" The Scotchman raised his brows with surprise.

"Not really. I associate them vaguely with the sea and ships."

"So far, so good," granted the elder man.

"But the trouble is that's as far as I can go," Christopher said.

"Bless me!" ejaculated McPhearson.

"I meant once to find out all about chronometers; but before I got
started something interrupted me and I forgot it. I wasn't much
interested in them anyhow, I'm afraid."

"And now you'd like a few points, eh?"

"Yes. I know I shall get a great deal better idea of them if you tell
me," was the reply.

"If you weren't an American and I a Scotchman, I should say you were an
Irishman," laughed his companion.

"Why?" demanded Christopher innocently.

"Because you sound as if you had kissed the Blarney Stone. Well, if you
wish to learn about chronometers you have chosen a somewhat difficult
subject. It leads pretty far, you see. However, I will do my best to
give you at least a few facts about them. In the first place the earth
actually revolves on its axis in twenty-three hours, fifty-six minutes,
and four seconds. We commonly divide our day, however, into twenty-four
hours and let it go at that. But astronomers reckon more accurately.
They call our day the solar day and instead of having a clock with
twelve figures on it as we do, they use one with twenty-four."

Christopher glanced up with a smile.

"Why be so fussy about things like minutes and seconds?"

"Because sometimes such things as minutes and seconds make a great deal
of difference. You may remember that when we were talking of sundials I
told you they were not exact timekeepers."

"I do remember."

"You see, we reckon our day by two counts: one of them begins at noon
and goes on--one, two, three, four o'clock, etc.--up to midnight; the
other begins at midnight and ends at noon."

"That's simple enough. I get that all right."

"Now people didn't always do that. There were other countries that
planned their day differently. The ancient Babylonians, for instance,
began their day at sunrise; the Athenians and Jews at sunset; and the
Egyptians and Romans at midnight."

"How funny! I thought that of course it had always been done as we do
it," confessed Christopher, with frank astonishment.

"Not at all. Our present system of time-keeping has been evolved out of
the past and, like many other such heirlooms, is the result of a vast
amount of study.