T. MIZTJNO. 



The difference between tlie results of this and those of the last 

 experiment I am inclined to ascribe to the diffraction effects of electric 

 waves caused by the plate. 



Experiment 8. 



A rectangular wooden board, 69 cm. in length and 14 cm. in 

 breadth, was coated all over with tinfoil. When it was held vertical- 

 ly with the longer edges parallel to the primary oscillations, the resis- 

 tance of my tinfoil grating placed behind it shewed no change, but 

 when the edges were placed perpendicular to the primary oscillations, 

 I found : — 



This shows that the intensity of the diffraction effect depends on 

 the extension of the tinfoil board with respect to the direction of the 

 primary oscillations. 



Experiment 9. 



A parabolic cylinder exactly similar to the one mentioned before 

 was placed against the latter, at a distance of about 1*5 m. So that 



