ILLUSTRATING THE DOT AND THE DASH.--To illustrate: Let us suppose, for convenience, that the downward movement of the lever in the key, and the bar in the sounder, make a sharp click, and the return of the lever and bar make a dull click. In this case the ear, after a little practice, can learn readily how to distinguish the number of downward impulses that have been given to the key. _The Morse Telegraph Code_ A . - N - . & . ... B - ... O .. 1 . - - . C .. . P ..... 2 .. - .. D - . . Q .. - . 3 ... - . E . R . .. 4 .... - F . - . S ... 5 - - - G - - . T - 6 ...... H .... U .. - 7 - - .. I .. V ... - 8 - .... J - . - . W . - - 9 - .. - K - . - X . - .. 0 ---- ------ L -- Y .. .. M - - Z ... . EXAMPLE IN USE.--Let us take an example in the word "electrical." E L E C T R I C A L . -- . .. . - . .. .. .. . . - -- The operator first makes a dot, which means a sharp and a dull click close together; there is then a brief interval, then a lapse, after which there is a sharp click, followed, after a comparatively longer interval, with the dull click. Now a dash by itself may be an L, a T, or the figure 0, dependent upon its length. The short dash is T, and the longest dash the figure 0. The operator will soon learn whether it is either of these or the letter L, which is intermediate in length. In time the sender as well as receiver will give a uniform length to the dash impulse, so that it may be readily distinguished. In the same way, we find that R, which is indicated by a dot, is followed, after a short interval, by two dots. This might readily be mistaken for the single dot for E and the two dots for I, were it not that the time element in R is not as long between the first and second dots, as it ordinarily is between the single dot of E when followed by the two dots of I. CHAPTER X HIGH TENSION APPARATUS, CONDENSERS, ETC. INDUCTION.--One of the most remarkable things in electricity is the action of induction--that property of an electric current which enables it to pass from one conductor to another conductor through the air. Another singular and interesting thing is that the current so transmitted across spaces changes its direction of flow, and, furthermore, the tension of such a current may be changed by transmitting it from one conductor to another. LOW AND HIGH TENSION.--In order to effect this latter change--that is, to convert it from a low tension to a high tension--coils are used, one coil being wound upon the other; one of these coils is called the primary and the other the secondary. The primary coil receives the current from the battery, or source of electrical power, and the secondary coil receives charges, and transmits the current.