4268. The time when the sun is on the meridian or at the noon-mark is also given to the nearest second, for every day in the year. This affords a ready means of obtaining correct time and for setting a clock by using a noon-mark, adding or subtracting as the sun is slow or fast.
4269. Old-fashioned Almanacs, which use apparent time, give the rising and setting of the sun's centre, and make no allowance for the effect of refraction of the sun's rays by the atmosphere. The more modern and improved Almanacs, which use clock time, give the rising and the setting of the sun's upper limb, and duly allow for refraction.
4270. Velocity of Sound and Light.—Sound moves about thirteen miles in a minute. So that if we hear a clap of thunder half a minute after the flash, we may calculate that the discharge of electricity is six and a half miles off.
4271. In one second of time—in one beat of the pendulum of a clock—light travels over 192,000 miles. Were a cannon ball shot toward the sun, and it were to maintain full speed, it would be twenty years in reaching it—and yet light travels through this space in seven or eight minutes.
SIGNS OF THE WEATHER.
4272. Dew.—If the dew lies plentifully on the grass after a fair day, it is a sign of another. If not, and there is no wind, rain must follow.