ACTION OF A BEAM OF LIGHT ON THE EYES 45 



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 pene- 

 trate 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 



