The fifth paper of this series (1930) was the author's last, after which the work was handed over to L. H. N. Cooper. It was resumed by the author in 1948 to compare the early years with the post-war, since the determinations had lapsed. Measurements of the extinction coefficient of the water were also resumed, and it was desirable to obtain the chemical data at precisely the same time.

The phosphate results are, as before, expressed as P2O5 in mg./m.3, since for crop calculations this old unit is convenient; to convert to mg. P, which is more rational, multiply by 0437; to bring to milligram atoms multiply by 0–0141. The analyses have not been corrected for salt error, since the early results were not^ and the factor for this correction has not as yet been agreed upon.

The silicate results are given as mg./m.3, of SiO2, but though the standard used in Plymouth was checked for me by Dr E. J. King in Canada and agreed with his (King & Lucas, 1928), yet a different value had to be assigned to the silica factor of the picric acid solution. All values have accordingly been multiplied by I.44.

The phosphate results for E1, surface, from 11 February 1948 to 1 February 1949 are shown in Fig. plotted against the dates.