— 69 — COUNCIL -MARCH 1920 -APPENDIX 



For 12 hr. periods ^/g hr. observations — Range of directions over 46°; speed from 



71/2 to 15 cm/sec. 

 For 12^/2 hr. periods ^/g hr. observations ■ — Range of directions over 59°; speed 



from 6Y2 to 14 cm/sec. 

 For 13 hr. periods ^/g hr. observations ■ — Range of directions over 70°; speed from 



4^/4 to 14 cm/sec. 

 The terminal points have been plotted and are marked B on attached diagrams. 

 A series covering from the evening of 1st August to the afternoon of the 

 4th August 1913, taken hourly, at the Varne lightship was next taken and resul- 

 tant vectors were prepared for series of 12, 12^/^, 13, 25, and 37^2 hours at -/g 

 hourly intervals. 



These gave the following variations: — 

 For 12 hr. periods. Range of direction 137°. Speed range 12.5 cm/sec. from 3.1 



to 15.6 

 For 12^2 hr. periods. Range of direction 111°. Speed range 12.6 cm/sec. from 2.6 



to 15.2 

 For 13 hr. periods. Range of direction 106°. Speed range 14.5 cm/sec. from 1.9 



to 16.4 

 For 25 hr. periods. Range of direction 37°. Speed range 5.9 cm/sec. from 3.7 to 9.6 

 For 37^/2 hr. periods. Range of direction 34°. Speed range 2.3 cm/sec. from 5.5 



to 7.8. 

 It is interesting to note that for the full 2 weeks observations of which these are 

 a portion the resultant is given as about N 60 E, 4 cm/sec. whereas over the 3 

 tides taken it would appear to be between E and S 60 E and from 5^2 to 7^/4 cm/sec. 

 This rather points to some influence which was dominant at some considerable 

 portion of the remainder of the 2 weeks period. 



Turning now to the diagrams marked B for positions H 2 and Varne it will 

 be seen that there is a tendency for the consecutive resultants to swing more or 

 less in a spiral, but I am unable to account for this. It seems obvious that in working 

 up resultants, just a full tide period should be taken, but as this period is variable, 

 dependent upon moon, sun and wind, the latter cause makes it impossible to deter- 

 mine accurately the variabihty. Three periods, 12, 12^/2 and 13 hours, were chosen 

 and of the patterns made the 12^/2 is perhaps the most regular, but the progressive 

 spiral movement is distinctly traceable in all of them and even in the 25 and 37^/2 

 hour periods. It seems probable, however, that after eliminating the swing of the 

 tide the resultant tide is still in the nature of a spiral and if that is so it follows 

 that any series of observations which does not allow for the waxing and waning 

 of the spiral would be subject to very large probable errors. In order to determine 

 the dimensions of the spiral it would be necessary to have continuous observations 

 at a fixed spot for much longer periods. 



To sum up, the resultant tides based upon a single day's observations are 



