AND NEIGHBOURING SEAS DURING 1897. 215 



winds were calculated independently in each case in terms of pressure, 

 by constructing a polygon of forces from each set of data, the length of 

 each line being made proportional to the sum of the wind pressures 

 from the corresponding quarter. The records on the Beaufort scale and 

 those in terras of velocity were reduced to terms of pressure by means 

 of the following table* of equivalents : — 



Force, Beaufort scale . .01234567 8 9 10 11 12 

 Velocity, miles per hour . 3 8 13 18 23 28 34 40 48 56 65 75 90 

 Prcssjtrc, pounds per foot . 0-05 0-3 0-8 15 2-5 4 6 8 11-5 15 21 28 40 



This method is founded on that employed by Dr. Fulton f in his report 

 on the drift-bottle experiments of the Scottish Fishery Board, but differs, 

 for reasons already stated, in the employment of terms of pressure in- 

 stead of terms of " force " for the construction of the polygon. The 

 practical result of this change is easily seen from the following examples: 

 — On Fulton's method a wind of force 9 is regarded as only 3 times as 

 effective (in the production of currents) as a wind of force 3 ; by using 

 terms of pressure, however, the same wind is regarded as 10 times as 



effective ^— = loV Similarly on Fulton's method a wind of force 8 is 

 only twice as effective as one of force 4; on mine it is regarded as 

 between 4 and 5 times as effective (t^ = 4"6). 



In the case of the Prawle winds the observations taken daily at 8 

 a.m. and 6 p.m. were used, for Plymouth those at 9 a.m. and 9 p.m., 

 while at Falmouth the hourly records were used, amounting to 73 in all 

 for this period of drift. As the bottle was put overboard at 3 p.m. on 

 April 22nd, and recovered at 4 p.m. on the 25th, half the wind-pressure 

 on the evening of the 22nd was combined with half the pressure on the 

 morning of the 25th in the Prawle and Plymouth cases. The results, 

 as determined by the length of the resultant line in the polygons, was 

 as follows : — 



Prawle Point — Resultant sum of Pressures = 38 -j 



Plymouth ... Ditto ditto = 15-5 / ^^^^^ °" ^ observations daily. 



Falmouth ... Ditto ditto =767 „ 24 „ „ 



Dividing the Falmouth resultant by 12, in order to put it on a par 



* This is the table authorised by the Meteorological Office in 1875 after the publication of 

 Scott's paper, with the addition of a tabic of pressure-equivalents. The latter are com- 

 puted from the velocities by multiplying the squares of the velocities by the factor O'OOS, 

 and expressing the results as far as possible in whole numbers. A more recent table of 

 velocity-equivalents by Jlr. Curtis {Quart. Join: Met. Sue, XXIII., 1897), has been kindly 

 forwarded to me by Mr. Scott, but reached me too late for use in tlie present report. It 

 differs from Mr. Scott's table in assigning somewhat lower velocities to all the figures of 

 the Beaufort scale. 



t Fifteenth Annual llqwrt of the S.F.B., Fart III., 1897, p. 357. 



