The Boy with the U. S. Weather Men Part 11

Let's get the meridian plane, first. Dan'l, do you suppose there's a pail of whitewash in the barn?"

"Yas, suh," the darky replied, "Ah knows there is."

"Go ahead and get it then," the observer asked, "and let me have a piece of string."

He fastened the string to the bottom of the pole and awaited the return of Dan'l with the whitewash. In a moment the old negro came back with the pail.

"Now," said the Forecaster, "I'm going to hold this string right at the end, and, holding it tightly, walk around the pole. What kind of a figure will that make?"

"A circle," answered the two boys.

"Right. Dan'l, you take the brush and whitewash a narrow line right behind my hand as I move the string round."

Dan'l stooped down and rapidly painted in the circle, as the Forecaster moved the string.

"Next," said the Weather Man, "we'll make another circle, a little closer in."

"At any special distance, sir?" asked Anton.

"No," was the reply. "It doesn't matter. Any distance at all will do."

A second, and again a third circle was thus made.

"Tie a piece of rope around the pole," was the next direction, "as high as you can reach."

This only took a minute.

"Now, boys," the Forecaster said, "all that you have to do is to watch when the shadow of the rope crosses those three circles. Put in a peg this evening when it crosses the inside one, then the middle and then the outside. To-morrow morning, mark with pegs the place where the shadow crosses the same circles on the other side, only, of course, it will cross the outer one first."

"Then what shall we do, sir?" asked Anton.

"Have you a long straight board?" he asked in reply.

"Plenty of them," the younger lad answered.

"Good. Well then, to-morrow morning lay that board so that its edge touches the two points where the shadow of the rope on the pole crossed the outer circle and let Dan'l whitewash a straight line joining the two points. Do the same with the second and with the inside circles."

"Yes?" queried the lad eagerly, "and then?"

"You'll have three parallel lines," the Forecaster said, "the outer one longer and the next two shorter. Bisect those lines. Do you know how to do that?"

The younger lad shook his head.

"Only by measuring with a bit of string and doubling the string," he said.

The Forecaster took a pencil and an envelope out of his pocket.

"It's quite simple," he explained. "Fasten a string to the peg at one end of the line you want to divide in half. Stretch the string along the line till you come to the end of this line. Then make a circle. Do the same thing from the other end of the line. That will give you two circles crossing one another. With the board, draw a straight line joining the points where the circles cross.

"To be exact, bisect the line on the middle and on the inner circles in the same way. You'll find they all come out the same. The bisecting line, reaching from the pole, and crossing the bisected lines is called the plane of the meridian. If I were you, I'd make that line a permanent mark by pressing into the ground a row of stones, or those white clay marbles. Then the rain can destroy the other whitewash lines, without doing any harm, because you've got what you were after."

"But how is that going to show the time?" queried Ross.

"Because," said the Forecaster with a smile, "whenever the shadow of the pole lies along the line of white marbles, which marks the meridian plane, it is exactly twelve o'clock by sun time."

"Without any measuring as to length?"

"Without any measuring at all."

"That ain't no clock, Mistah Levin," the darky announced in a superior way. "Ah don't hold with no clock like that."

"Why not, Dan'l?"

"Ah gets hungry other times besides noon," he said. "Ah'd only eat once a day by that clock. No, suh, Ah wants a clock that tells every hour o'

the day, not jest noon-time.

"Ah got another clock that don't never need no mending, not in summer-time," continued Dan'l. "My marigolds open at seven sharp every mornin' an' wink their eyes at me an' say 'Dan'l, yo're hungry,' and Ah sho' is. An' jest before six o'clock in the evenin', the white moon-flowers say, 'Dan'l, time fo' supper and yo' little white bed.' An'

dey's right, too. Don't need no sun-clocks."

"I'm like Dan'l," put in Anton, "I'd like to be able to tell every hour, not just twelve o'clock only!"

"Well," the Forecaster answered cheerfully, "you can make your sun-clock that way if you like."

"Can we, sir?" asked Anton. "How?"

"By using your pole as the style or upright of a sun-dial. Before clocks were invented, people told the time by sun-dials, and there was a whole science of sun-dials, called gnomonics. It was quite a difficult mathematical science. Even after clocks and watches came into use, sun-dials continued to be used as time-pieces, because watches and clocks were expensive and there were few mechanics who could mend them."

"I've been wondering--" began Anton.

"Let's make a sun-dial here, Mr. Levin?" asked Ross, finis.h.i.+ng Anton's sentence. "We can, can't we?"

"Certainly. You can make a sun-dial anywhere. If you had to do it without a watch, you might find it a little difficult, of course, but it can be done. For example, I can tell you off-hand that for this lat.i.tude here, the angle between noon and eleven o'clock, is a little over nine degrees, while it is nearly ten degrees at New York.

"Since you've got a watch, however, it's quite easy. Your meridian line marks twelve o'clock, and a line drawn at right angles to it, from the base of the pole, inclined to an angle corresponding to the lat.i.tude, will mark six o'clock, morning and evening. If you'll put in a peg on the circle that Dan'l whitewashed, exactly at the place where the shadow touches when it is one o'clock, two o'clock and so forth on your watch, the watch having been made to agree with the shadow at noon, your sun-dial will be right all the year, round. You don't need to mark anything earlier than four in the morning or later than eight in the evening, as even on the longest day, here, the sun does not rise before that time nor set after it. You don't have to get up before six o'clock to mark the hours, as the lines are the extension of the four and five lines of the afternoon."

"Let's do it!" cried Anton. "We'll make a clock with white stones, just that way! Couldn't I divide it up into five minute distances, like a regular clock, Mr. Levin?"

"Yes," the Forecaster answered, "if your circle is big enough. And if you wanted to do the thing in the way that it used to be done, you could have a little motto running all around the circle, just picked out in white stones."

"What kind of a motto, sir?"

"All kinds were used," the other answered, "I remember one that read 'Pa.s.s On'; another 'Do not linger'; but the one I like best is the old Latin one which ran 'I count only the bright hours.' I suppose you've heard the story of the American sun-dial motto?"

"No, sir," said both boys together.

"You knew that the sun-dial is one of the official emblems of the United States?"

"I never heard of it," Ross exclaimed.