=How Time Is Distributed.=—In this country the correct standard time is sent out by the United States Naval Observatory at Washington to all cities east of the Rocky Mountains, by _wire telegraph_, and all over the Atlantic ocean and seaboard by _wireless telegraph_. [Illustration: FIG. 166.—STANDARD TIME AT DIFFERENT CITIES.] When time is received over the wires from Washington it is distributed by local telegraph or by _time balls_ to various jewelry stores and to private citizens who always want to be set right. How an astronomer gets the correct time; how it is sent out over the wires and by wireless and how it is distributed to the common people is a mighty interesting piece of business. Briefly it is like this: =How Correct Time Is Obtained.=—Every observatory has, besides its big telescopes, a _transit instrument_, a wonderfully accurate _clock_, and a clockwork device called a _chronograph_. The transit instrument is nothing more than a telescope with a thin piece of clear glass with a number of lines ruled on it with a diamond, about ⅛ inch apart, and this ruled glass is set between the eyepiece and the object glass, as shown in Fig. 167. [Illustration: FIG. 167.—RULED GLASS IN TRANSIT INSTRUMENT.] This telescope, or transit instrument—so called because it is used to observe the _transit_, or passage, of a star across a meridian—is set on an axis so that the telescope can be pointed to any place on the meridian but it cannot be moved east or west. Sometime before a star is due to cross the meridian the astronomer sets his transit instrument so that the star will pass right across the line of sight of his telescope. The purpose of observing the transit, or passing of a star is to see how much his wonderfully accurate clock has lost or gained during the past 24 hours. So his clock is right at hand. The chronograph is another accurate clockwork which revolves a cylinder about the size and shape of a phonograph cylinder, and around which is wrapped a sheet of white paper. This cylinder makes one revolution every minute. A fountain pen marks a spiral line on the paper when the cylinder is revolving but at every second the pen is thrown out of position and this makes a notch in the line. After starting the chronograph the astronomer takes an electric push button, which is connected with and controls the lever which holds the pen of the chronograph that makes the notches, and takes up his position with his eye at the end of the transit instrument. The instant he sees the star on one of the lines in the telescope he presses the button and this closes the electric circuit and makes a big notch in the line traced on the paper of the chronometer. From the position of the big notches which he caused to be made on the paper as the star crossed the ruled lines, and the little notches made regularly every second, he can dope out just how much his clock is in error—that is, how much it is too fast or too slow.