346 Mr. F. Gal ton on the Conversion of 



a navigator to estimate by simple measurements the probable 

 duration of a proposed passage. The wind- charts compiled by 

 the Meteorological Department of the Board of Trade are seldom 

 used by navigators ; for they do not afford the results that sea- 

 men principally require ; they only give data from which those 

 results might be calculated by some hitherto unexplained pro- 

 cess, which, we can easily foresee, must be an exceedingly tedious 

 one. 



To convert wind-charts, or the tables of wind-direction from 

 which the wind-charts have been compiled, into passage-charts, 

 we must ascertain the distances that ships of different classes 

 would attain in an hour, if they made the best of their way 

 under the same wind towards different points of the compass. 

 With a moderate wind, a merchantman of the class that usually 

 navigates the Atlantic will, by beating to windward, make 24 

 miles an hour, right in the wind's eye. At two points off the 

 wind it will make 3 miles ; at four, 4 miles ; at six, 7 miles ; at 

 eight, 8 J miles ; at ten, 9 miles ; at twelve, 9J miles ; at fourteen, 

 8J miles; and at sixteen, or with the wind right astern, it will 

 make 1\ miles. We must next turn to the wind-charts, or to 

 the Tables from which they were compiled, to ascertain the pro- 

 portion of the winds that blow from different points of the com- 

 pass, in the region we are investigating. Thus in one particular 

 case we find, out of one hundred observations, that six referred 

 to N. winds, fourteen to N.N.E., seventeen to N.E., six to 

 E.N.E., three to E., two to E.S.E., two to S.E., five to S.S.E., 

 six to S., six to S.S.W., six to S.W., three to W.S.W., three 

 to W., three to W.N.W., four to N.W., five to N.N.W., and 

 nine calms. The force of the winds was not recorded in this 

 instance; we must therefore, for want of better information, 

 assume them to be moderate. We have now to calculate the 

 progress that ships could make towards each point of the com- 

 pass, under the several influences of each of these winds. In 

 the example taken, the N. wind will be reckoned as lasting 6 

 per cent, of an hour, and therefore ships would be able to sail 

 during its prevalence, *014 mile to the N., *018 to the N.N.E., 

 and so on. The N.N.E. wind lasting 14 per cent, of an hour 

 will enable ships to sail '042 mile to the N., '033 mile to 

 N.N.E., and so on, The N.E., E.N.E., and all the other winds 

 would have their influence similarly calculated. We thus obtain 

 a Table of sixteen lines (not reckoning the line of zeros that cor- 

 respond to " calms") and of sixteen columns, whose addition 

 gives the total progress of one particular class of ships, in one. 

 hour, to all points of the compass, under the influence of the 

 winds that blow in the ocean-district under consideration. 



