318 Intelligence and Miscellaneous Articles. 



If the poles of the battery are reversed there is only a small 

 deflection ; it seems that the illumination of the positive armature 

 is not effective. 



It is clearly the action of the ultra-violet radiation which pro- 

 duces here the flow of negative electricity, as in the experiments 

 cited, the layer of air acquires a kind of unipolar conductivity. 



I have repeated these experiments with batteries of 1 to 100 

 elements. For two Daniells, the distance of the disks being 2 to 

 3 millim., the deflections are 30 to 50 divisions, 1 division corre- 

 sponding to 9xl0 -11 amperes. With 100 zinc-water-copper 

 elements traces of a current are obtained even with disks separated 

 by 10 centim. 



Cleaning the solid disk increases the effect. The intensity of 

 the arc has great influence. In order to investigate the laws of the 

 phenomenon the arc must be kept constant and the comparisons 

 be made as quickly as possible. 



By observing these precautions I arrive at the following con- 

 clusions ; — 



(1) If the surface illuminated is diminished (by covering J, 

 J, | of the gauze with a screen) the current diminishes in pro- 

 portion. 



(2) When the distance I of the disk is varied the current varies 

 also ; but it is not inversely proportional to Z, and it seems rather 



to follow the law i— — . 



a+bl 



(3) When the electromotive force E which charges the disk is 

 increased the current constantly increases ; so long as E is small 

 (to two Daniells) it is proportional to it, and then increases more 

 slowly. The apparent resistance of the layer of air seems thus to 

 increase with the electromotive force. 



If the two disks are of different metals, their electrical difference 

 must be allowed for in estimating the electromotive force. The 

 proportionality of i to the external electromotive force is then 

 masked by the difference in question. If the total electromotive 

 force makes the solid disk positive there is no effect. 



This suggested to me the idea that a current might be obtained 

 in any circuit even without a battery, provided the gauze be of a 

 metal more positive than that of the solid disk. Thus, with a disk 

 of perforated zinc as gauze, and a solid disk of silvered copper, I 

 obtained a current. This is a kind of element where the illumi- 

 nated air takes the place of liquid, and which acts as long as the 

 illumination lasts, the current being maintained at the cost of the 

 radiant energy. When the two disks are brought closer until they 

 finally touch, the current increases to a certain limit, it then passes 

 through zero, and changes its sign (thermoelectric effect). 



By comparing the current in the condenser zinc-silver with that 

 which one Daniell produces, I have arrived at a value of 0*97 to 

 1-06 volt for the difference Zn/Ag. This is accordingly a galvano- 

 metric method, for comparing the electric differences of metals, 



