452 Prof. G-. Melander on the Production of Statical 



One half of the glass rod was ground and the other 

 half smooth, but both parts were by exposure positively 

 charged. 



Experiments on the electrification of metals by exposure 

 are attended with very great difficulties, as is also the case 

 with electrification by friction. The metal must be held by 

 means of some insulator, and it is difficult to distinguish 

 between the charge on the metal and that on the insulator. 

 A few experiments with brass spheres showed that brass is 

 negatively charged by heating. Other metals were perhaps 

 positively charged, but the effect is much smaller than in the 

 case of insulators. 



The action of sunshine seemed even in summer to depend 

 on the degree of cloudiness of the sky, and as in autumn 

 the altitude of the sun began to decrease, the charge pro- 

 duced also diminished, and in some cases it was observed 

 that in the morning the lower sides of the paraffin plates 

 were positive, though in the course of the day they became 

 negative again. Later on in the year pieces of paraffin 

 which were kept in the darker places about the laboratory 

 showed a constant positive charge ; this was never observed 

 in summer, paraffin wax being then, as mentioned before, 

 always more or less negatively charged. It was also re- 

 marked that during two very sunny weeks from the 1st to 

 the 15th October all the paraffin plates, even those in the 

 darker parts of the room, showed a negative charge. 



As in winter the action of daylight became continually 

 weaker, I tried to obtain a source of artificial light which 

 would serve to charge the plates. 



A Bunsen flame, whether luminous or not, has not the 

 slightest influence on paraffin, even when near enough to 

 melt it, but if the plate is previously charged its charge is 

 diminished by the heating. Plates exposed for a long time 

 to strong arc light showed a slight negative charge, but it 

 is doubtful whether this might not be due to the direct 

 influence of the potential of the arc terminals. Opportunity 

 was also obtained of trying a powerful Finsen lamp, and a 

 mercury- vapour lamp with a quartz tube, but no appreciable 

 effect was observed. 



The active rays are specially strong in sunlight and are not 

 stopped by a glass window. I have tried to find out whether 

 the plates after exposure gave signs of radioactivity. The 

 experiments were made with an electroscope of the Societe 

 centrale des produits chimiques of Paris, which is specially 

 constructed for investigations on radioactive bodies. The 

 apparatus was, however, not sensitive enough for this purpose, 



