1915- ^O- 2. SPITSBERGEN WATERS. 85 



just before the first quarter of the moon, which occurred on August 19th. 

 This may also make some difference but hardly of great importance. 



As the distance to Port ^*i^go from the edge of the continental shelf 

 outside (to the westi is shon. only about 12 miles (22 kilometresl. it is 

 hardly probable that the tidal wave should reach this place much later 

 than the station of our obervations to the north. If we assume the average 

 depth to be 50 metres between the edge of the shelf and Port Virgo, and 

 450 metres between the sea west of Port Virgo and the station of our 

 observations, about 80 kilometres to the north, the tidal wave should reach 

 this station and Port \'irgo nearly simultaneoush-. 



The difference of a little more than three hours, found between high- 

 water at Port \ irgo and high-water at our station to the north, is conse- 

 quently noteworthy. It is striking that this difference seems to be very 

 nearly equal to a quarter 13 hours and 6 minutes! of a semidiurnal tidal 

 period. 



The series of current-measurements which Helland-Hansen took on 

 Storeggen (outside Aalesund in Norway), on July 12th and 13th, 1906. 

 shows, however, similar peculiarities when compared with the time of high- 

 water at Christiansund. As Mr. Werner Were.vskiold points out in a 

 paper on the subject he is now writing, high-water occurred at Helland- 

 Hansen's station on Storeggen. about 4 hours 48 minutes earlier than at 

 Christiansund. the distance between the two places is 176 kilometres, and 

 the tidal wave may travel this distance in about i" 42^ if the average 

 depth be about 85 metres. This leaves a period of about 3h 6^. which 

 high-water came comparatively earlier on Storeggen than at Christiansund. 

 Mr. Werenskiold's explanation of this apparent discrepancy is that high- 

 water at the two places occurs at two different phases of the tidal wave. 

 Over the deep sea, high-water occurs when the crest of the tidal wave 

 passes the place, with maximimi surface velocity in the direction of the 

 propagation of the wave, while on a coast, with shallow water outside, 

 high-water occurs at a later phase of the wave, midway between crest and 

 trough, at the change of the tidal current, when it is slack. Hence it follows 

 that the difference in time between the two high-waters should be a quarter 

 of the semidiurnal tidal period, or about 3 hours and 6 minutes. 



Though our current-measurements are not sutTiciently complete to give 

 exact results in the above respect, they prove, however, that by methodic 

 researches of this kind, carried out from a steadily drifting ship, moored 

 to the drifting ice (or kept by drift ar.chorsi, the tidal currents may be con- 

 veniently studied over the deep ocean. 



