"But let us return to Dionysius. His idea of making the year begin on the 25th of December was thought to be rather too inconvenient, and so the old commencement on the first day of January was retained, as the Romans had arranged it. But the plan of Dionysius was carried out with regard to the numbers by which the years were to be named and called. Thus the year which had been known as 754 became, under the new system, the year 1. And the succession of years from that year 1 is called the Christian era. To get the numbers of its years you have only to subtract 753 from the years in the Roman numbering."
"If we add 753," said Joe, "to 1880, will we get the number of years since old Rome was founded by Romulus and Remus?"
"Yes," said the Professor; "the rule works both ways. There is, however, some uncertainty as to whether the Romans themselves were correct in regard to the age of their city. Very early dates are hard to settle."
"Where did the months get their names?" asked May, "and how did months come to be thought of at all?"
"The months were suggested by the moon. In most languages the word month is very nearly like moon, as you see it is in ours. From new moon around to new moon again is about twenty-nine days, which is nearly the length of a month. The exact time between two new moons is a very puzzling problem. It always involves a troublesome fraction of a day, and is, in fact, never twice alike. So it was found convenient to divide the year into twelve parts, nearly equal, and to call each one a month."
"Why didn't they make them just equal?" asked Gus.
"To do so would have made it necessary to split up some of the days, which would have been awkward. If you divide the 365 days of the year by twelve, there will be five remaining."
"How was it found out that the year had 365 days in it?" asked Joe.
"It took the astronomers to do that," said the Professor; "and until nations became civilized enough to study astronomy accurately, they did not know the number of days in the year. This, however, did not prevent them from being able to count the years, because they could know that every time summer or winter came, a year had passed since the last summer or winter. But now the length of the year—that is, the time occupied by the earth in going completely round the sun—is known within a fraction of a second."
"Was it worth while to go into it so precisely?" asked May. "Would it not have been enough to know the number of the days?"