When fish-shoals moving about in their vertical zone at night arrive at a definite intensity of illumination accidentally, they begin to crowd toward the light source. The form of the range of crowding depends chiefly upon the intensity curve of the source and the size of the range, upon the turbidity of sea water and the intensity of the source. The intensity of illumination on the limiting surface of the range is nearly constant, so it is possible to measure the size of crowding by the visible depth of Secchi disk vertically under the source. If the visible depth of Secchi disk be expressed by z, the depth of the lower limit of crowding vertically under the source by D and the amount of crowding fishes by ν, then the following relations hold:
D∞z² and ν ∞z³.
Crowding fishes move, in a group, round about the vertical line through the source very calmly for a few hours, but they are scattered and lost when the intensity of the source suddenly changes.
At the present time in Japan, petroleum burners, of which the intensity is 750 -1, 100 candles and the rate of petroleum consumption 7.5-9.0 litres per hour, are used for net-fishing and crowding fishes are caught by means of a few kinds of nets like purse seine (Nuikiri-ami, Aguri-ami, Kintyaku-ami etc.).
The development of this fishery, nowaday very stagnant, seems to be able to result only from the invention of a more economical and more scientific lamp which may give a steady illumination and collect the crowding fishes within a desirable range.

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Against the treatise “On Standard Illumination Intensity of Factory” by Mr. Gansei Doi, the auther describes the following facts and the reason:
1. The luminous intensity at working plane is not to be determined referring to the relation between light and fatigue only, but it must be chiefly considered about the relation be tween illumination and eye sight from the practical point of view.
2. It is most suitable for the practical cord to provide the minimum intensity and the recom mended intensity.

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