"That comes after the cyclone," explained Anton. "A 'low' means that the pressure of the atmosphere is less than usual, and, consequently, doesn't press the mercury up so far in the barometer. The air weighs less, that shows that it must be expanding. The winds in front blowing into a 'low' are generally warm winds. When a 'low' is traveling fast, with a 'high' or 'anti-cyclone' behind, the colder winds come rushing forward to take the place of the rising warm air and they bring colder weather with them. The freeze comes during the early clearing weather of a 'high,' before the anti-cyclonic winds--which blow in the opposite direction, the way of the hands of a clock--have had a chance to steady down." "Then," said the farmer shrewdly, "if you get reports of wind and of barometer from points to the west and northwest, you can tell when a cold wave in on the way. Is that it?" "Exactly," the Forecaster replied. "We cannot always tell, of course, when the weather is going to be a little colder or a little warmer, but a cold wave, serious enough to damage crops and property, can always be foretold. Remember your storm tracks again. In this county, in the State of Mississippi, we are very unlikely to get a freeze, unless there is a rapidly moving 'low' passing up towards the Ohio and St. Lawrence Valleys followed by an equally energetic 'high' plunging down from the Canadian Northwest." "And can you always tell what the weather is like, all over the country?" "Yes, indeed," the Forecaster answered. "There are two hundred official stations scattered all over the United States and the West Indies, each one carefully selected because its site is a key station to weather changes. Twice a day, exactly at eight o'clock in the morning and eight o'clock in the evening, the observations are taken at each station." "And have they all got rain gauges like mine?" asked Anton. "Yes, all of them." "And wind-measurers, like my anemometer?" queried Tom. "Yes," the Forecaster agreed with a smile, "and some of them have devices that make a continuous record of wind velocity." "And barometers like mine?" put in one of the younger boys, not to be outdone. "Various forms of barometers, and barographs, and thermographs, and sunshine recorders and all sorts of things. Some of them even have seismographs, which tell of every tiny little earthquake, that may be going on all over the world. You know, boys, there's hardly an hour of the day that there isn't a small earthquake, somewhere, and there are really quite sizeable earthquakes at least once a month. A well-equipped weather office is quite a complicated affair, and it takes well-trained men to conduct the observations and interpret them properly." "All those observations are sent to Washington, aren't they, sir?" queried Anton. "Just as I send mine every night to Bob, for him to transmit by wireless."