"Very good. Now, Mr. Tighe, you can see from the map that the barometric pressure, the isobar, running through this part of the country shows a barometric pressure of 30.30. From what Anton told you, it is easy to see that, the day before yesterday, Issaquena County was still in the grip of the tail end of a 'high,' with a high barometric pressure—five points above the low in Salt Lake City—with a cold temperature, and with a wind blowing outwards from the 'high' or anti-cyclone. Is that clear?"
"Clear as well water," the farmer declared.
"Now," said the Forecaster, "let us look at yesterday's map for eight o'clock in the morning. Here, just over the Canadian border, right at Medicine Hat—as though to make good the old proverb—is a vigorous 'high,' with a barometer of 30.50, with a temperature of 20° below zero and with the winds blowing outward from the centre. The 'low,' which the day before yesterday was central over Salt Lake City, yesterday was central over Oklahoma City. It has, therefore, traveled over five hundred miles in the day. On all sides of the 'low' there is rain, and you remember how it rained here, yesterday morning, early?"
"Indeed I do," said Jed Tighe. "I didn't get out on the land until nearly eleven o'clock."
"Now what was the temperature here yesterday morning, Anton?" the Forecaster queried.
"Forty-six degrees," answered Anton promptly, for he had been expecting the question.
"Ten degrees warmer, you see, Mr. Tighe, as the 'low' came nearer. And what was the wind, Tom?"
"South-south-east," the lad answered, his note-book in hand.
"Showing," the Forecaster explained, "that during the twenty-four hours, Issaquena County had lost the effect of the 'high,' which has disappeared from the map, and was fully in the grip of the oncoming 'low.' Now, if you look at the map, Mr. Tighe, you'll see that the isobar for this region shows a barometer pressure of 29.50, a terrific drop of four points in twenty-four hours. No wonder it rained!"
The farmer bent over the map, his eyes glued on the lines which suddenly seemed to spring into life before him.