"Down over the country comes this 'low,' at the rate of five hundred miles a day, with rain and moist winds accompanying it, and sharp on its heels, racing from the north, comes the cold 'high' which we have just seen forming at Medicine Hat. The cold wave is fully organized and is on its way." He laid the third map on the table. "Here is the situation at eight o'clock this morning," he said. "The 'low' or storm, has swung at right angles, following the preferred Ohio and St. Lawrence Valley Route. It left Toledo early this morning and at eight o'clock was raging over the Great Lakes, with its centre north of Buffalo. It is speeding up, you see, having traveled eight hundred miles since yesterday. The cold wave 'high' from Medicine Hat has traveled along its usual track and is now central over Kansas, with clear skies and a drop of thirty degrees in temperature. There was a severe freeze in Kansas last night, with zero temperatures, and freezing point was touched on the Mexican border." "Whew," whistled the farmer, "and is that on its way here?" "It is," the Forecaster answered. "Your temperature?" he continued, turning to the boy. "Thirty-seven," Anton answered. "Going down rapidly, you see. The wind, Tom?" "Northwest." "Blowing outwards from the rapidly approaching 'high.'" "What's the barometer?" asked the farmer, who was quickly grasping the manner of reading a weather map. "It has gone up again to 30.02. The cold wave is coming fast. Since Dodge City, Kansas, is about five hundred miles from here, and since the 'high' is traveling at about seven hundred miles a day, and as, moreover, there is generally a slight slowing up as it makes the turn, the centre of the 'high' ought to strike us here about six o'clock tomorrow morning. The cold wave, however, is in advance of the centre, so Mr. Tighe, you need to be prepared for a cold wave tonight. "If you ship your potatoes this afternoon, as you planned to do, they would meet severe weather and might get frozen. If you ship them tomorrow, you might be safe, but you couldn't be sure, because the 'high' is turning northwards and therefore its eastward distance is not so great. If you ship them on Monday you would be safe, but even then you could not ship them to New York, for a fast train might overtake the tail of the cold wave. On Tuesday you can safely ship them to any part of the United States." The farmer stepped back from the table and his eye roved over the boys. "And was that the way that you lads figured out that my fruit was likely to be frozen?" he asked. "Yes, sir," said Anton, "that was how." "It's a marvel," the farmer declared. "I don't see why more people don't use these Weather Maps."