On Ionization and Wifeless Telegraphy. 381 



(3) The resistance change on illuminating a selenium 

 block is always greater when used in a bridge o£ the second 

 type. The change in conductivity throughout a thin layer 

 at the illuminated surface of a homogeneous block is in- 

 sufficient to explain this phenomenon. 



(4) The effect of light on selenium blocks, the effect of 

 filing the surfaces, and the dependence of the resistance on 

 the nature and pressure of the electrodes, on the voltage and 

 on certain other conditions, all point to the existence of a 

 high resistance at the contact of the selenium and the 

 electrodes. 



(5) The action of light on all selenium bridges is to a 

 large extent, but not wholly, to effect a change of resistance 

 at the electrode contact. 



(6) Films of selenium can be obtained by " cathode dis- 

 integration/' If the deposit is received on a plate at a 

 suitable temperature, the films are continuous and light- 

 sensitive. 



The above experiments were carried out in the Physical 

 Laboratory of the University of Bristol under the direction 

 of Dr. A. M. Tyndall, to whom I desire to express my best 

 thanks for much advice and help throughout the work. 



Nov. 22nd, 1913. 



XXXIX. On Ionization and Wireless Teleqrapliy. 

 By E. H. Barton. D.Sc, F.R.S.E* 



FROM the paper on the above subject by Prof. Howe f, 

 it would appear that the relation between the theory 

 of Dr. Eccles and some experiments recently carried out 

 by E. H. Barton and W. B. Kilby % was not made quite 

 clear. This short note is accordingly offered in explanation. 

 In the work referred to no direct attempt was made to 

 detect, either (1) any increase in velocity of wave propagation 

 or (2) any special kind of conductivity which might be con- 

 cerned with such increase. Neither was it claimed that any 

 such effects had been sought for or detected. 



The position was simply this. The theory of Eccles as to 

 the propagation of electric waves in ionized air involved 

 (what may be termed) an ordinary and an extraordinary 

 effect — the first being the conductivity and the second 

 beino- the increase of velocity of wave propagation. In 

 order to test this theory experimentally, it was natural 

 to try first if the ordinary effect (the conductivity) was 



* Communicated by the Author. 



+ Phil. Mag. Jan. 1914, pp. 213-215. 



X Phil. Mag-. Oct. 1913, pp. 567-578. 



