266 Mr. F. Galton on Meteorological Statistics [Apr. 24, 



amount when we have 16. In calculating to only 4 points, we have, as is 

 shown in Table III., no more than 4 lines and 4 columns, or 4 2 = 16 entries. 

 If we dealt with 8 points, the number of entries would amount to 8 2 = 64, 

 and if with 16, to 16 2 =256 entries ; but the amount of labour involved in 

 such tedious computations need excite no apprehension, because I shall 

 show how calculation may be entirely dispensed with, and the results 

 obtained by the aid of a machine with remarkable facility and quickness. 



Table III. 



Course 

 of ship. 



Helativ 

 N. 



30 per cent. 

 Force 3. 



3 frequency { 

 E. 



25 per cent. 

 Force 2. 



ind force of 

 S. 



15 per. cent. 

 Force 1. 



wind. 



w. 1 



10 per cent. 

 Force 2. 



Total 

 miles on 



each 

 course. 



N. 



Wind ahead, 

 point. 



720 miles. 



Abeam, 

 8 



950 



Astern, 

 16 



180 



Abeam, 

 24 



d80 



2230 



E. 



Abeam, 

 24 



2670 



Ahead, 

 



250 



Abeam, 

 8 



180 



Astern, 

 16 



340 



3440 



S. 



Astern, 

 16 



2370 



Abeam, 

 24 



950 



Ahead, 

 



75 



Abeam, 

 8 



380 



3775 



w. 



Abeam, 

 8 



2670 



Astern, 

 16 



850 



Abeam, 

 24 



180 



Ahead, 

 



100 



3800 



We, have thus far supposed no current to exist ; if there should be a 

 current, the above contour would be incorrect as regards the position of 

 A ; but it would be perfectly correct in regard to the position in which a 

 float would be found at the end of the day which had been dropped in the 

 water at the beginning, because the float and the ship would have drifted 

 simultaneously in parallel lines. If, then, A be the point of departure 

 and A' be the position of the float at the end of the day, and if we 

 ;draw a contour, as described above, round A', it will be true for the 

 joint effects of winds and currents for A. Conversely, in order to con- 

 struct a contour for their joint effects from A, we have first to draw A A' 

 to represent the drift of the current in one day from A, and then to use 

 A' as a point of construction for a contour calculated upon the data of the 

 winds alone; the contour so drawn will be the required figure, with A 

 "for the point of departure. 



