178 On the Determination of Wave-length of Electric Radiation. 



The diameter of the central ball = O78 cm. 



each side bead = O3 



Distance between the outer surfaces of the beads = 1'5 cm. 

 ?J inner (sparking) surfaces ,, = 0'9 



The wave-length, 1*84, is almost exactly equal to twice the distance 

 between the sparking surfaces of the beads. Without further ex- 

 periments with different sized radiators, it is difficult to say whether 

 the above simple relation is accidental or not. The following rough 

 determinations, made with a second radiator, may be of some interest 

 in connexion with the above. I took off the central sphere from the 

 radiator used in the last experiment, and substituted a larger ball. 

 The distance between the inner sparking surfaces is then 1'2 cm. 



Breadth of Strip = 3 cm. 



The wave-length found is approximately equal to 2*36 cm., and 

 twice the distance between the sparking surfaces is 2*40 cm. 



Conclusion. The experiments described above seem to prove that 

 the diffracted spectrum is not continuous, but linear. The method 

 of determining the wave-length of electric radiation by diffraction 

 grating is seen to give results which are concordant. The deter- 

 minations are not affected by the periodicity of the receiving circuit, 

 the receiver being simply used as a radioscope. With a better 

 mounting and a finely graduated circle, it would be possible to obtain 

 results with a far greater degree of accuracy. I hope to send, in 

 a future communication, the results obtained with a better form of 

 apparatus, with which I intend to study the relation of the wave- 

 length with the size of the radiator, and the influence of the enclosing 

 tube on the wave-length. I shall at the same time send an account 

 of transmission gratings. 



