Data obtained during the cruises of the s.ss. Huxley and Oithona in the years 1903 to 1906 indicated a general seasonal movement of water into and out of the mouth of the English Channel. It was found that in the autumn, somewhat sooner or later and to a greater or less extent each year, water, of the high salt content characteristic of the open Atlantic in the north of the Bay of Biscay and to the south-west of the English Channel, began to move in a north-easterly direction into the mouth of the English Channel, extending in a tongue along the centre of the Channel and into the Irish Channel, which is characterised by water of lesser salt content.

This general movement of relatively high salinity water continued during the winter until the spring or early summer, when water of lesser salinity moved southward from the Irish Channel across the mouth past Ushant, and to some extent into the English Channel; the condition in August being that water of relatively high salinity which had entered the Channel during the winter months was cut off from Atlantic water of equal salinity by a less saline water-mass extending south from the Irish Channel.

These general movements have been deduced from the data collected during the cruises in February, May, August, and November. To accurately depict the changing conditions and follow the movement of the water year by year would require frequent observations, more or less simultaneous, over a wide area—a condition of perfection which in practice could not be obtained without the use of several ships working almost continuously and in conjunction.