In order to establish a practical method of measuring the aerodynamic size distribution of any aerosol sample collected by a 4 stages cascade impactor, the theoretical consideration and calculation of collected proportion of particles by using a computer were attempted on the basis of the theory of Ranz & Wong and the assumption on the log-normal distribution for aerosol samples, for 345 kinds of particle size distributions having 23X15 paramaters.
In the calculation, the approximation to the partial collection efficiency for each stage of cascade impactor was introduced for simplifying the calculation and for applying the method easily to any type of cascade impactors.
The result from the calculation was arranged by relative quantities of collected particles on each stage and indicated as a ready-reckoner. In practice, we can obtain the geometrical-mean-diameter (Da₅₀) and the geometrical standard deviation (σ) of a given sample of aerosol, by measuring the collected quantities of the aerosol on each stage of cascade impactor (particle number, mass, activity etc, of the collected sample) and by searching the best fitness of the values to the one among 345 kinds of size distribution which were calculated by the computor in advance. This procedure could be easily accomplished by using the ready-reckoner above-mentioned.
As actual size distribution of many aerosols are said to be subjected to the log-normal distributions, the method above-mentioned is considered to have enough accuracy in practical used and to obtain better approximation for particle size distributions in general.

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Experimental studies were made on particle size distribution of wood fibre ground by disk type refiner. Refiner used was Bauer type double rotating disk refiner sized 915mm in diameter.
Particle sizes were measured by standard sieves and their distribution constants n were correlated with the densities of experimental woods. From the experiments, it was found that with increase of the apparent density of wood ρw decreases the value of n.
Experimental relation was n=0.28ρ_w^-1.2
By the above relation, together with the experimental data on power consumed in disk type refiner, it became possible to evaluate the particle size distribution of wood fibre as a function of power consumption of disk type refiner.

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