The flags used for army signalling are only two in number if we consider their design, though, as each of these is made in two sizes, the actual outfit consists of four flags. The large size is three feet square, and the smaller is two feet square; the larger sizes are clearly more visible, but on the other hand the smaller save weight and consequently labour; and with good manipulation and clear weather their messages can be followed by observers, with ordinary service telescopes, up to a distance of twelve miles or so. The poles are respectively five feet six inches long and three feet six inches, and the flags themselves are either white with a blue horizontal stripe across the centre, or wholly blue. Only one flag is used at a time, the first being used when the background is dark and the second when light, so as to ensure under all circumstances the greatest visibility. The person sending the signals should hold the flag pointing upwards to the left, and with the pole making an angle of about 25°, with an imaginary vertical line passing down the centre of his body. The signals are based upon the dot and dash system of Morse. The dot or short stroke is made by waving the flag from the normal position to the corresponding point on the right hand, while for the dash or long stroke the flag is waved till the head of the pole nearly touches the ground. The Morse alphabet is so constructed that the letters of most frequent occurrence are represented by the shortest symbols, and no letter requires more than four of these for its expression, while figures are all represented by five signs. {128} The letters of the alphabet are thus represented:-- A ·- A (æ) ·-·- B -··· C -·-· D -·· E · F ··-· G --· H ···· I ·· J ·--- K -·- L ·-·· M -- N -· O --- O (oe) ---· P ·--· Q --·- R ·-· S ··· T - U ··- U (ue) ··-- V ···- W ·-- X -··- Y -·-- Z --·· Ch ---- The following code is adopted to represent figures:-- 1 ·---- 2 ··--- 3 ···-- 4 ····- 5 ····· 6 -···· 7 --··· 8 ---·· 9 ----· 0 ----- A space about equal in length to the dash is left between each letter, and a time interval of about three times the duration between each word. This alphabet, once learned, it is evident can be utilized in many ways. Steamers, by means of short and long whistles, can spell out messages to each other; seamen, across a harbour, can communicate by waving their arms; prisoners by opening and shutting their hands. It is also utilised in the light-flashes of the heliograph, in telegraphy again, and in various other directions.