the experiment may succeed, the rays must be directed, not towards the object, but towards the eye, there can be no question here of an increase in emission of a luminous body influenced by "N" rays, but indeed of a strengthening of the effect upon the eye, due to the "N" rays which are superposed on the luminous rays.
This fact astonished me all the more because, since the slightest film of water arrests "N" rays, it seemed unlikely that they could penetrate into the eye, whose humours contain more than 98.6 per cent. of water (Lohmeyer). The small quantity of salt contained in these humours must have rendered them transparent to "N" rays. But, then, in all probability, salt water must itself be transparent. Experiment shows that this is the case, for while a sheet of wet paper completely arrests "N" rays, a vase of Bohemian glass, 4 cms. in diameter, filled with salt water and placed in their path, lets them pass without sensible weakening. A very small quantity of sodium chloride is sufficient to render water transparent. What is more, salt water is capable of storing-up "N" rays, and
