In part 1, the influence of back qround picture to the qeometrical visual illusions of the test figures was studied. As a result of feature extraction, the color of picture was expressed by lightness, chroma and hue, and the geometrical figure by the degree of fineness of texture. Investigation of the interaction between test figures and the features to visual illusion has shown that only texture was significant. Average back ground picture gave smallest visual illusion, and fine textured picture gave the largest one. The influence of the test back ground pictur is larger when control back ground picture was constant. Size of picture width needs more than 4 times width of the test figure.

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The relationship between the flame retardancy of polyester (PET) fibers and Bromine (Br) and Phosphorus (P) contents in PET fibers was investigated with widely varied mutual ratios of both components as a fundamental study on the flame retardation of PET fibers.
Comparing the affinities of Br and P to PET fibers, the former was considerably higher than the latter, that is, PET fabric treated with saturated solutions containing either Br or P showed that retained amount of P was 1/9-1/10 that of Br though the concentration of P in treating‘bath was 1/2 that of Br.
Nither Br nor P alone gave any sufficient flame retardancy, but combination of a slight amount of P, even less than 0.1%, with Br showed sufficient flame retardancy when Br content was 6.5% or more. Lower Br contents required higher P contents for satisfactory flame retardation, but considerable improvement of flame retardancy was observed with only a slight amount of P if Br content was kept at a certain level. Such phenomena clearly evidenced the synergistic effect of Br and P. In every case, Br acts as a dominant factor probably because of higher retention of Br on PET fabric.
The synergistic effect of Br and P was also reflected in the flame retardancy at higher environmental temperatures such as a simulated fire spot, that is, samples containing both Br and P showed less reduction of the flame retardancy at higher environmental temperatures as compared with the results obtained from the unfinished sample and those finished with compounds containing Br or P alone.

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