This paper describes fundamental formulas concerning water disinfection by means of a germicidal lamp, and their comparison with experimental data. The formulas show the relation between the average survival ratio of micro-organisms and several varied factors, such as depth of water, absorption coefficient at the wavelength of 253.7mμ, ultraviolet irradiance, lethal energy of the micro-oranisms, exposure time, and the rate of flow of running water.
Reference data for design of a water disinfector is described, also.

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The author had looked for “The Coefficient of Final Illumination of Interreflection” in the solution of integral epuation for the interreflection, that indicates the illumination distribution of the sqherical wall. This paper explained the relations between the coefficient of final illumination of interreflection and other coefficients. To inquire into this coefficient, we may say, is nothing but to study the general theory of integrating sphere itself.
It was prooved that the kernel of solution of integral equation, that is to say, the ratio of Fredholm's minor to Fredholm's determinant, has physical meaning, that is, illumination of the window that was measured when the lumen per unit solid angle makes the way in any direction.
This is no more than tha coefficient of final illluination of interreflection, that the author has defined the other day. The calculated result of this coef f iccient coincided with the experimental result which was measured by turning a ream of light.
In inquiring into this coefficient of final illumination of interreflection, it is convenient, as was stated in “Joural of the Illuminating Engineering Institute of Japan vol.42. No.10. PP. 450, ” if one likes to check many characteristics of integrating sphere, without solving the integral equation.

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