抄録
The under-water illumination at Lake Abashiri on August 23, 1947, was measured by the methed of Pearsall and Hewitt (1933), using potassium iodite solution. However, the concentration of sulphuric acid in the solution was slightly increased.
The diurnal variation of intensity of under-water illumination at various depths was given in Fig. 3. The intensity of light at the depth corresponding to the limit of Secchi's disc reading (1.3 metres in the present case) was about 7.3% of that obtained at the layer just under the surface.
