TRANSACTIONS OF THE SECTIONS. 17 



gical Department. The weather under which a ship enters a division may be of 

 any description whatever, except that of an absolute cahn in a sea without a cur- 

 rent, and therefore has no bearing- on the present question. It must furtlier be 

 observed that the error he had pointed out not only alfects the winds, but all the 

 meteorological elements so far as they are correlated with the winds ; the tempe- 

 ratm'e and dampness are especially aft'ected by it. The method he proposed by 

 which this error might be obviated, was to impose a limitation to the observations 

 in respect to interval in distance, in addition to the existing- eight-hourly interval in 

 respect to time. He proposed that observations slioidd not be included in the groups, 

 unless the places where they were made were at least as far asunder, measuring 

 in the direction of the ship's general course (and not along- her tacks) as she could 

 traverse with a favom-able -wdnd in eight hours. Then on an average not more 

 than three observations would be accepted from a single log-book in any 5-degree 

 ocean square. He did not possess data to show how far the accm'acy of the exist- 

 ing wind charts is impaired by the neglect of this cause of error. He presumed 

 that it would only be in certain parts of the ocean that it would exercise consider- 

 able influence on the computed proportions of the winds, but that the ratio of the 

 calms would be everywhere exaggerated. It was sufficient that he should point out 

 the error as one to be guarded against for the futm-e, for he trusted that the whole 

 of the work in the Meteorological Office would be submitted to recomputation, 

 and that an improved method of handling and grouping the observations would be 

 adopted, in accordance with the recommendation of that Report to which he had 

 already alluded. 



On the Conversion of Wind-charts into Passage-charts. 

 By Francis Galton, F.E.S. 



The most direct line between two points of the ocean is seldom the quickest 

 route for sailing-vessels. A compromise has always to be made between directness 

 of route on the one hand, and the best chance of propitious "winds and cm-reuts on 

 the other. Hence it is justly argued that an inquiry into the distribution of the 

 winds over all parts of the ocean is of high national importance to a seafaring 

 people like ourselves. A knowledge of the distribution of the winds would clearly 

 enat)le a calculation to be made which would show the most suitable passage in any 

 given case. 



But as a matter of fact, no calculations have yet been made upon this basis ; much 

 less have charts been contrived to enable a navigator to estimate by simple mea- 

 surements the probable duration of a proposed passage. The wind-charts compiled 

 by the Meteorological Department of the Board of Trade are seldom used by navi- 

 gators ; for tliej do not afford the results that seamen principally require ; they only 

 give data fi'om v.-hich those results might be calculated by some hitherto unex- 

 plained process, 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 2g 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 eio-ht, 

 85 miles : at ten, 9 miles ; at twelve, 9^ miles ; at fourteen, 8f miles ; and at six- 

 teen, or -with the wmd right astern, it vdll make 7^ miles. We must next turn to 

 the wind-charts, or to the Tables from which they were compiled, to ascertain tlie 

 proportion of the winds that blow from different points of the compass, in the re- 

 gion we are investigating. Thus in one particular case we find, out of one hundred 

 obser-\ 



SIX 



to 



N.W., five to N.N.W., and nhio calms. The force of the winds was not recorded 

 in this instance ; we must therefore, for want of better information, iissume them 

 to be moderate. We have now to calcidate the progTess that ships could make to- 

 1866. 2 



