Page:On the Strain Theory of Photographic Action.djvu/9

1901.] Touch" I have given similar instances of reversals produced by the action of long-continued electric radiation.

10. Other Methods of obtaining Latent Image.

If molecular strain be the basis of all photographic phenomena, then it ought to be possible to obtain latent images by other methods of producing molecular strain.

An instance of this is seen in the development of mechanical pressure marks. Images produced by electric strain are seen in the "inductoscripts."

11. Conclusion.

It is thus seen—

(1.) That molecular strain is produced by the action of light.

(2.) That as the physico-chemical properties of a substance are changed by strain, it is possible to develop the latent image through the difference in the following properties between the exposed and unexposed portions produced by light—

(a.) Difference in adhesive power, e.g., development of daguerreotype by mercury vapour, development by water vapour.

(b.) Difference in chemical stability, e.g., development by reducing agents.

(3.) That molecular strain may not only be produced by visible or invisible radiation, but also by (a) electric induction, (b) mechanical distortion. Latent images produced by such means may be developed, e.g., inductoscripts, development of pressure marks.

(4.) That nearly all substances are sensitive to radiation, but the effect cannot in all cases be rendered visible, (a) owing to want of suitable chemical developers, (b) owing to quick self-recovery. The molecular effect due to radiation can, however, be demonstrated by the conductivity or electromotive variation methods.

(5.)That the latent period of overcoming inertia corresponds to the photographic induction period.

(6.) That the relapse of image is due to self-recovery.

(7.) That owing to the tendency towards self-recovery the radiation effect does not solely depend on the total quantity of light, but depends also on the time-rate of illumination. Hence the photographic effects of intermittent and continuous illuminations are not the same.

(8.) That the continuous action of radiation produces recurrent reversals.

(9.) That the molecular effects produced by light and electric radiation are similar.

VOL. LXX.