The appearance of the electric arc of welding is sketched looking through seven different protecting glasses for welding.
The absorption spectra of the filters are observed by naked eyes. Photographic observation of such absorption spectra are often useless to investigate the property of coloured glasses or filters, because the spectral sensitivities of photographic plates are much differ from that of eyes.
It takes some time for an eye to distingish objects when the eye is covered by a dark filter. The time for the seven different filters are compared. And also it takes some ume for an eye for the disappearance of the residual image formed by a strong welding arc light. The time for the seven different filters are compared.
All observations are done by 13 observers, men and wernen of different age.
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