for Voltaic Electricity and on the Electric Light. 1 5 



4. Among the metallic oxides great differences of conducti- 

 bility exist. Those which are opake and endowed with lustre, 

 are in general better conductors than the others. M. Necker 

 has noticed this circumstance. 



5. The same remark applies to the metallic sulphurets. 



6. The chlorides are in part conductors and in part insulators. 



7. The same variety exists among the salts. The great majo- 

 rity of them are insulators. 



8. The molecular state determines the conductibility or non- 

 conductibility of the same substance. Diamond insulates, gra- 

 phite conducts well. 



9. Among the minerals of vegetable origin, the more perfect 

 the carbonization the better the conductibility. 



10. Among the conducting minerals which do not crystallize 

 regularly, some present differences of conductibility when the 

 direction of the current through the mass is varied. 



Professor Wartmann has recently made some experiments with 

 the electric light*, with a view of testing its applicability as a 

 means of public illumination. To render the light constant, an 

 instrument constructed by Duboscq for the adjustment of the 

 coal points was made use of. With a pile of 50 couples of 

 Bunsen he obtained a light intolerable to the naked eye ; his 

 assistant, indeed, by incautiously looking at the light, had his 

 eyes inflamed to such a degree as to render it necessary to bathe 

 them several times with warm water before they could be opened. 

 In the first experiment the flame of a candle and that of a jet of 

 gas cast very distinct shadows upon a screen. At a distance of 

 250 metres the light reflected from a mirror competed success- 

 fully with that of a jet of gas. 



A second experiment was made under conditions still more 

 decisive. In this experiment the descending rain and the 

 absence of houses deprived the light of all auxiliary splendour. 

 Nevertheless on concentrating its rays on a slightly divergent 

 cone, by means of a concave glass mirror 0*4 of a metre in dia- 

 meter, it was found that the hght was equal to that of 300 large 

 gas-jets at least. At 100 metres, notwithstanding the rain, it 

 was possible to read distinctly. The experiment was made before 

 the hydraulic engine-house in Geneva, and from the higher 

 windows of the hotel and the neighbouring houses the persons 

 taking part in the experiment could be recognized. The light 

 was cast upon the fa9ades of the quay, and its reflexion was 



* Note sur quelques Experiences faites avec le Fixateur Electrique, 

 par M. le Prof. Elie Wartmann. — Bibliotheque Universelle, Aug. 1852. 



