Wave-length of Electric Radiation by Diffraction Grating. 177 

 Grating B. Breadth of strip = T5 cm. 



Grating C. Breadth of strip = 2 cm. 



Grating D. Breadth of strip = 2'5 cm, 



Grating E. Breadth of strip = 3 cm, 



It would thus be seen that the different values of wave-length 

 obtained from the above experiments are concordant, the mean value 

 being 1*846 cm. 



I then carefully removed the electrical vibrator, and measured 

 approximately the size of the sparking balls. The radiator, it must 

 be remembered, was placed vertically inside a square tube, each of 

 whose sides is 2'5 cm. The radiator was about 1 cm. inside from the 

 free end of the tube. 



