SUMMARYMeasurements were made, throughout the year 1928, of the penetration of daylight into sea-water in the English Channel. One vacuum and two gas-filled potassium photo-electric cells were used below water. In all save the first series an efficient diffusing surface was used with the photometers so that the corrections for obliquity of illumination, necessary in our earlier work, were rendered almost negligible. From October onwards a more sensitive gas-filled cell was available for use, together with a more powerful amplifier and a more efficient insulation of the high-tension batteries; improvements in the switching of the photometers on and off were also incorporated.The following conclusions have been reached :—1. The conclusions put forward tentatively in 1928, concerning the agreement between the vacuum and gas-filled cells, have been substantiated in the main, although the vacuum photometer, which is relatively more sensitive to the blue end of the spectrum, generally indicated rather higher opacities.2. There are no regular seasonal changes in the opacity of the water. A very high opacity occurred in the autumn of 1927, but this was not repeated in 1928.3. On one occasion, in April 1928, an unusual degree of clearness of the water has been shown to have been associated with the influx of water of lesser salinity, from further out in the Channel. The clearness of the water at El in December, 1927, and September, 1928, is probably due to an influx of clearer water, though the salinity changes indicating this are not so well marked.

No abstract

. MATTHEWS (1916MATTHEWS ( , 1917 was the first to observe that in early summer the surface water of the sea just outside Plymouth Breakwater is almost completely devoid of phosphate, owing to its utilization by algffi, fixed and planktonic. Brandt (1916-20) using Raben's (1916 analyses noted, in the Baltic especially, a minimum phosphate content in June, but this minimum was far from denoting complete exhaustion.Later, Atkins (1923,'25,'26), using methods of analysis entirely different from those employed by Matthews or by Raben, obtained results in close agreement with those of Matthews, and showed that even twenty miles out to sea, at the International Hydrographic Station E1, the surface water was entirely deprived of phosphate in summer. As the season advanced the deeper water became at first very much poorer in phosphate and later on rather richer again, according as this salt was used up by the phytoplankton and then regenerated by the decay of animal and plant cells and by the excretion of animals. It was further shown by Atkins and Wilson (1927) that Brandt's curve did not indicate complete exhaustion of phosphate because the method of analysis employed included arsenic, originally present as arsenite, but oxidised to arsenate and precipitated with the phosphate. Reasons were adduced for the belief that the amount of arsenic present in the sea as arsenate is very minute and is all used up in summer by the algffi. It is doubtful whether any analyses yet made have distinguished the trace of arsenate, if indeed it exists, from phosphate.Since the phosphate content of the various species of the phytoplankton, mainly diatoms, may be assumed to be similar, a study of the phosphate changes affords a measure, in an inverse ratio, of the production of the algal crop, and indicates from year to year the variations that occur in its seasonal waxing and waning. Such studies have shown that between the spring outbursts of activity as much as two months' difference may be noted in successive years. The variations

On account of the minute quantities in which they are present and of the fact that they are considered of secondary importance as indicating sewage contamination, phosphates are not usually estimated in analyses of natural waters. The tediousness of the determination also militated against it in the past. As a result, of the numerous analyses recorded by Clarke (1920), but few mention phosphates. C. H. Stone's analysis of the Mississippi in 1905, carried out upon a sample above Carrolton, Louisiana, shows 0.27 per cent of phosphate (PO4) with a total salinity of 146 parts per million, or 0.39 mgrm. PO4 per litre, corresponding to 0.29 mgrm. P2O5.

Sea water collected at Station E1, surface, between June 1948, and November 1949, contained suspended matter from 2·77 to 0·45 g./m.3 (or parts per million) dried and ignited. A few determinations of insoluble organic matter gave 1·77 to 1·15 parts per million dry weight at 100° C. The ignited residue contained from 55 to 17% silica, 28 to 3 of ferric oxide, 20 to under 1 of alumina and 70 (or excluding one high value 29) to 9 calcium carbonate. There was nothing in the records for temperature or salinity to suggest that the water mass had changed during the period of sampling.The analyses reveal an unsuspectedly large amount of iron, compared with that found in solution. The ignited residue is rich in silicate, judging from the silica alumina ratio, but it is quite doubtful whether the additional supply of silicate available for diatoms is at all adequate to balance their requirements calculated on a phosphate utilization basis. It seems more probable that a considerable amount of the phosphate is available for non-siliceous phytoplankton.