45 X 45 = 2025 / 200 = 10.125; or, 45 X 45 - 2025 X .005 = 10.125. Again, twenty-five miles per hour would be 25 X 25 = 625; and this multiplied by .005 equals 2 pounds pressure. CONVERTING HOURS INTO MINUTES.--It is sometimes confusing to think of miles per hour, when you wish to express it in minutes or seconds. A simple rule, which is not absolutely accurate, but is correct within a few feet, in order to express the speed in feet per minute, is to multiply the figure indicating the miles per hour, by 8 3/4. To illustrate: If the wind is moving at the rate of twenty miles an hour, it will travel in that time 105,600 feet (5280 X 20). As there are sixty minutes in an hour, 105,600 divided by 60, equals 1760 feet per minute. Instead of going through all this process of calculating the speed per minute, remember to multiply the speed in miles per hour by 90, which will give 1800 feet. This is a little more then two per cent. above the correct figure. Again; 40 X 90 equals 3600. As the correct figure is 3520, a little mental calculation will enable you to correct the figures so as to get it within a few feet. CHANGING SPEED HOURS TO SECONDS.--As one- sixtieth of the speed per minute will represent the rate of movement per second, it is a comparatively easy matter to convert the time from speed in miles per hour to fraction of a mile traveled in a second, by merely taking one-half of the speed in miles, and adding it, which will very nearly express the true number of feet. As examples, take the following: If the wind is traveling 20 miles an hour, it is easy to take one-half of 20, which is 10, and add it to 20, making 30, as the number of feet per second. If the wind travels 50 miles per hour, add 25, making 75, as the speed per second. The correct speed per second of a wind traveling 20 miles an hour is a little over 29 feet. At 50 miles per hour, the correct figure is 73 1/3 feet, which show that the figures under this rule are within about one per cent. of being correct. With the table before you it will be an easy matter, by observing the air pressure indicator, to determine the proper speed for the anemometer. Suppose it shows a pressure of two pounds, which will indicate a speed of twenty miles an hour. You have thus a fixed point to start from. PRESSURE AS THE SQUARE OF THE SPEED.--Now it must not be assumed that if the pressure at twenty miles an hour is two pounds, that forty miles an hour it is four pounds. The pressure is as the square of the speed. This may be explained as follows: As the speed of the wind increases, it has a more effective push against an object than its rate of speed indicates, and this is most simply expressed by saying that each time the speed is doubled the pressure is four times greater.