EECENT PROGRESS IN PHYSICS. 



421 



Unprepared carbon 



' Carbon with nitrate of strontium 



Carbon Avith caustic potash 



Carbon with cliloride of zinc 



Carbon with borax in sulph. acid 



932 

 139 



353 

 274 



160 

 75 



624 

 159 



1171 

 165 



This table shows that on increasing the distance of the points the 

 intensity of light and the force of current decrease. By most of the 

 substances with which the carbon had been prepared, the arc of light 

 was made more steady and allowed of a greater distance of the points, 

 but the intensity was not greater, except with the carbon prepared 

 with borax and sulphuric acid. 



But the results in the above table are only approximately accurate, 

 since the changeable position of the most brilliant points at the origin 

 of the arc may have prevented the light from acting with its full in- 

 tensity upon the photometer. In another series of experiments, an 

 abstract of which is given in the following table, this error was 

 avoided, the arc of light having been directed towards the photometer 

 by means of a magnet. In these experiments only 34 Bunsen's cups 

 were used, the distance of the carbon points was not changed, and the 

 intensity of the light was measured for different degrees of force of 

 current. 



Intensity of 

 liy:ht. 



Carbon with boracic acid. 



Carbon with sulpliate of soda. 



198 

 252 

 298 



178 

 203 

 34 6 

 460 



The carbon saturated with sulphate of soda was not heated to red- 

 ness before use. 



It follows from these experiments that the intensity of light in- 

 creases in a somewhat greater ratio than the force of the current. 



