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74 actions, the modification undergone by the luminous emission consist in a change in its distribution along the different directions comprised between the normal and the tangent plane to the luminous surface.

I have recently indicated that, whilst the action of "N" rays increases the quantity of light emitted by a phosphorescent screen in a normal direction, it diminishes the quantity of light emitted very obliquely (see the preceding communication). As is well known, heat also acts on phosphorescence, whose brilliancy it temporarily increases. When investigating whether this action of heat offered the same peculiarities as that of "N" rays, with regard to the direction of the emitted light, I found that, on the contrary, heat produces an increase in brilliancy in all directions comprised between the normal and the