89 
2. On the Tides in the Sound of Harris. By Henry C. 
Otter, Esq., B.N., Captain H.M.S. “ Porcupine.” Com- 
municated by Dr Stark. 
The author stated that during summer, in neap tides, the stream 
flows from the Atlantic into the Minch all day, but from the Minch 
into the Atlantic all night. In winter this was reversed, the stream 
flowing through the Sound of Harris from the Minch into the Atlan- 
tic all day, but from the Atlantic into the Minch all night. 
In spring tides, both during summer and winter, the stream 
comes in from the Atlantic during the greater part of the time the 
water is rising, and flows back into the Atlantic during the greater 
portion of the fall of the tide. 
The rise and fall of the tide was found to be much more influenced 
by the direction and force of the wind than by the moon’s parallax. 
Thus, a strong southerly or south-west wind raised the water to 
equinoctial height, but produced a very poor ebb. The velocity of 
the current through the Sound of Harris was stated to be about five 
o 
miles an hour during spring tides, but only from two to two and 
a-half miles an hour during neap tides. 
Various other interesting particulars were mentioned relative to 
the local peculiarities of the tides in the “ Narrows of Berneray,” at 
the “ Hermetray Group,” and at the “ Groay Group,” and a dia- 
gram was exhibited, by means of which the time of high water and 
low water could be easily found in the Sound of Harris, on knowing 
the moon’s meridian passage. 
Dr Stark, whocommunicated the paper, appended a note, endeavour- 
ing to account for the peculiarity in the current through the Sound 
of Harris, attributing it to a difference in the level of the water in 
the Atlantic and the Minch, caused by the attraction of the sun. 
So long as the sun was north of the equator, and its attractive power 
was greatest over the North Atlantic, the level of the Atlantic during 
the day would probably be found to be higher than that of the water 
in the Minch, so that during all the day the current would run from 
the Atlantic into the Minch ; during night, when the attractive 
power of the sun was removed from the North Atlantic, its level 
would fall, so that the stream would flow from the Minch into the 
Atlantic. In winter , when the sun was south of the equator, its 
VOL. IV. 
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