154 



Lieutenant Maury s Plan for Improving Navigation ; with 

 Remarks on the Advantages arising from the Pursuit of 

 Abstract Science. Extracted from Lord Wrottesley's 

 Speech in the House of Lords, on 26th April 1853. 



4 ' It is time that I should now explain how these charts are 

 constructed and routes discovered. The whole ocean is 

 divided into squares the sides of which represent 5° of longi- 

 tude and 5° of latitude ; in the midst of these squares the 

 figure of a compass is drawn, with lines representing sixteen 

 of the compass points, the intermediate points being omitted ; 

 the log-books are then searched for observations of the direc- 

 tions of winds and of the proportion of calms in each of 

 these squares. In the centre of each compass so drawn are 

 placed two numbers, one representing the total number of 

 observations obtained in the square, the other the percent- 

 age of calm days. By the side of each of the lines repre- 

 senting the sixteen points of the compass, are written num- 

 bers which denote the per-centage of the winds that have 

 been found to blow from that quarter, and at the extremity 

 of each line are numbers, which shew the per-centage of 

 miles a ship will lose if she attempt to sail 100 miles through 

 that particular square, in the particular direction indicated 

 by the line in question. Now that number is obtained as 

 follows : — 



" By the resolution of simple problems in sailing, it is 

 known that if the wind will not allow a ship to lie within six 

 points of her course, that is, if it be a head wind, she will lose 

 62 miles (omitting fractions) in every 100 that she sails, or, in 

 other words, after sailing 100 she will only have made 38 good 

 in the wished-for direction ; in like manner, if she can sail 

 within four points, she loses 2D miles, and if within two points, 

 only eight. Having therefore the per-centage of winds that 

 will make such deviation from the desired course necessary, 

 it is easy by a common proportion to calculate the total 

 amount of space lost or detour (as Maury calls it) for every 

 given direction, for every 100 miles sailed within the square. 

 When a course has to be traced, therefore, all the squares 



