How the Action of " N " Rays should be 

 observed 



It is indispensable in these experiments to 

 avoid all strain on the eye, all effort, whether 

 visual or for eye accommodation, and in no 

 way to try to fix the eye upon the luminous 

 source, whose variations in glow one wishes to 

 ascertain. On the contrary, one must, so to 

 say, see the source without looking at it, and 

 even direct one's glance vaguely in a neigh- 

 bouring direction. The observer must play 

 an absolutely passive part, under penalty of 

 seeing nothing. Silence should be observed 

 as much as possible. Any smoke, and es- 

 pecially tobacco smoke, must be carefully 

 avoided, as being liable to perturb or even 

 entirely to mask the effect of the " N " 

 rays. When viewing the screen or luminous 

 object, no attempt at eye-accommodation 

 should be made. In fact, the observer should 



