“YOU told us,” said Claire, “that at the same time the earth turns on its axis it travels round the sun.”

“Yes. It takes three hundred and sixty-five days for that journey; it makes three hundred and sixty-five pirouettes on its axis in accomplishing a journey round the sun. The time spent in this journey makes just a year.”

“The earth takes one day of twenty-four hours to turn on its axis; one year to turn round the sun,” said Jules.

“That is it. Imagine yourself turning around a circular table the center of which is occupied by a lamp representing the sun, while you represent the earth. Each of your walks around the table is one year. To represent things exactly, you must turn on your heels three hundred and sixty-five times while you circle the table once.”

“It is as if the earth waltzed around the sun,” Emile suggested.

“The comparison is not so well chosen as it might be, but it is exact. It shows that in spite of the giddiness of his age Emile has understood perfectly. A year is divided into twelve months which are: January, February, March, April, May, June, July, August, September, October, November, December. The unequal length of the months is sometimes confusing. Some have 31 days, others 30; February has 28 or 29, according to the year.”

“For my part,” said Claire, “I should find it hard to tell whether May, September, and other months have 30 or 31 days. How can one remember which months have 31 days and which 30?”

“A natural calendar, engraved on our hands, teaches us in a very simple way. Close the fist of the left hand. At the knuckles the four fingers, other than the thumb, from each a bump, separated by a hollow from the next bump. Place the index finger of the right hand in turn on these bumps and hollows, beginning with the little finger, and at the same time name the months of the year in order: January, February, March, etc. When the series of the four fingers is exhausted, return to the starting-point and continue naming the twelve months on the bumps and hollows. Well, all the months corresponding to the bumps have 31 days; all those corresponding to the hollows, 30. You must except February, answering to the first hollow. That has 28 or 29 days, according to the year.”

“Let me try,” proposed Claire. “We’ll see how many days May has: January, bump; February, hollow; March, bump; April, hollow; May, bump. May has 31 days.”

“It is as easy as that,” said her uncle.

“My turn now,” interposed Jules. “Let us try September: January, bump; February, hollow; March, bump; April, hollow; May, bump; June, hollow; July, bump. And now? I am at the end of my hand.”

“Now begin again and go on naming the months,” Uncle Paul instructed him.

“You go on at the same point where you began?”

“Yes.”

“All right. August, bump. There are two bumps in succession. There are then two months together, July and August, that have 31 days?”

“Yes.”

“I will begin again. August, bump; September, hollow. September has 30 days.”

“Why has February sometimes 28 and sometimes 29 days?” asked Claire.

“I must tell you that the earth does not take exactly 365 days to turn around the sun. It takes nearly six hours more. To make up these six hours that were disregarded at first in order to have a round number of days in the year, they are reckoned in every four years, and the additional day they make all together is added to February, which then becomes 29 days long instead of 28.”

“So, for three years running, February has 28 days, and the fourth year it has 29.”

“Exactly. Remember, too, that the years when February has 29 days are called leap years.”

“And the seasons?” queried Jules.

“For reasons that would be a little too difficult for you to understand yet, the annual journey of the earth around the sun causes the seasons and the unequal length of days and nights.

“There are four seasons, of three months each: spring, summer, autumn, and winter. Spring is from about March 20th to June 21st; summer from June 21st to September 22d; autumn from September 22d to December 21st; winter from December 21st to March 20th.

“On March 20th and September 22d the sun is visible 12 hours and invisible 12 hours, from one end of the earth to the other. The 21st of June is fo............