Platinum and Silver on the Luminosity of Phosphorus. 123 



be laid upon a wooden board, and the free end of a metallic 

 wire connected at its other end with the conductor of an 

 electrical machine be placed at the distance of a few lines be- 

 fore the dark phosphorus, the latter will become luminous as 

 soon as the electrical brush makes its appearance at the free 

 end of the wire; and in addition, a luminous tail of 4 to 6 

 inches long will be perceived behind the phosphorus. The 

 brush is no sooner made to disappear than the shining* tail 

 disappears also, whilst the phosphorus itself remains lumi- 

 nous for a second or two more. The brush being called forth 

 again, the phaenomena described will repeatedly take place. 



2. The same piece of phosphorus, at a temperature of 

 about 4° R. below zero, being placed within a coil made up 

 of one extremity of a copper wire, so that the end of that coil 

 projects (in the shape of a point) about a line beyond the 

 phosphorus, and the other end of the wire being connected 

 with the conductor of the electrical machine, a very interest- 

 ing phaenomenon will take place as soon as the brush is 

 caused to appear at the metallic point that projects beyond 

 the phosphorus. From the centre of the brush proceeds a 

 luminous cone, the apex of which lies in the middle of the 

 brush. The length of that cone varies with the size of the 

 brush, the longer the latter the longer the cone. I have often 

 obtained cones at least two feet in length with brushes being 

 hardly an inch long. I am sure the admirable machine of the 

 Polytechnic Institution would yield tails of extraordinary 

 length, and it is really worth while to make the experiment 

 with that powerful apparatus. I must not omit to mention 

 that the phaenomenon resembles exactly the tail of a comet, 

 and cannot be perceived but in complete darkness ; but it is 

 hardly necessary to add that the luminous cone disappears 

 invariably and simultaneously with the brush. If the finger 

 be approached to the brush so as to change the position of 

 the latter, the cone in its whole length is also put in motion. 

 In the experiments described use was made of the positive 

 brush ; in changing the positive electricity for the negative a 

 tail is likewise obtained, but that cone is thin and less lively. 



3. If, at a temperature of 2° R. below zero, a piece of 

 phosphorus be placed in a bottle so arranged that the elec- 

 trical brush may at pleasure be produced within that ves- 

 sel, the phosphorus becomes luminous so soon as the brush 

 makes its appearance, and that phosphorescence is the more 

 lively the stronger the brush and the longer the latter had 

 been made to play. The emission of light continues to take 

 place for a short time after the cessation of the play of the 

 brush. The phosphorus having grown dark, becomes lumi- 

 nous again along with the reappearance of the brush. 



