vi IMTRODUCTION. 



needle. All this could be taken in at a glance, and thus the young 

 mariner instead of groping his way along until the lights of expe- 

 rience should come to him by the slow teachings of the dearest of 

 all schools, would here find, at once, that he had already the expe- 

 rience of a thousand navigators to guide him on his voyage. He 

 might, therefore, set out upon his first voyage with as much con- 

 fidence in his knowledge as to the wmds and currents he might 

 expect to meet with, as though he himself had already been that 

 way a thousand times before. 



YI. But, to show the tracks of these vessels on a chart, a line 

 had to be drawn for each one ; now this, for so many, and all in 

 black or blue, and on the same sheet of paper too, would present, 

 it was perceived, a mass of lines in inextricable confusion. More- 

 over, after these tracks were projected, there would be no room left 

 for the name of the month to show when each one was made, 

 much less for any written account of the winds and currents daily 

 encountered by each vessel of the multitude. After the tracks 

 were projected, there would, it was found after trial, be barely 

 room left on the chart to write the name of the vessel, much less 

 the direction and set of the winds and currents. 



YIL An appeal, it was consequently decided, should be taken to 

 the most comprehensive sense of the five, and it was thereupon re- 

 solved to address all those tracks, and winds, and currents, with 

 their strength, set, and direction— in short, all this experience, 

 knowledge, and information — to the eye, by means of colors and 

 symbols. 



YIIL The symbols devised with this view w^ere a comet's tail 

 for the wind, an arrow for currents, Arabic numerals for the tem- 

 perature of the sea, Roman for the variation of the needle, contin- 

 uous, broken, and dotted lines for the month, and colors for the 

 four seasons. 



IX. A continuous line was used ip show that the track was 

 made during the first month ; a broken, the second ; and a dotted 

 line, the last month of each season : black standing for the winter, 

 green for spring, red fpr summer, and blue for autumn. 



X. The comet's tail, and the arrow, and the numerals, were also 

 in colors, according to the seasons. The force and direction of the 

 wind were indicated by the shape and position of this tail ; while 



