70 



Mr. J. H. Pepper on some Experiments [June 17, 



When the spark was received on the ice, it lost its flaming character, 

 and became thin and wiry, spreading out in all directions. 



If the discharging-wires were tipped with ice, the spark was always 

 flaming when any thickness of air intervened between thein. Even over 

 the ice, if the spark passed a fraction of an inch above the surface, it was 

 always a flaming one, but changed to the thin spark when the point of the 

 discharging-wire was thrust into the ice. 



If one of the discharging-wires of the great coil is brought to the centre of 

 a large swing looking-glass and the other wire connected with the amalgam 

 at the back, the sparks are thin and wiry, arborescent, and very bright (see 

 figure, p. 69), the crackling noise of these discharges being quite different 

 from that of the heavy thud or blow delivered by tbe flaming spark. 



When the discharging-wire is brought close to the frame of the looking- 

 glass, or if a sufficient thickness of air intervenes, the spark again becomes 

 flaming ; or, as sometimes occurs, if the discharging wire is placed about 

 5 inches from the frame, the spark is partly flaming and partly wiry, i. e. 

 when it impinges on the glass. 



The examination of the flaming spark with the spectroscope has not as 

 yet settled anything definitely. The spectrum is a continuous one with the 

 sodium-line. When the blast of air is used, and the wiry sparks made ap- 

 parent, then the nitrogen line appears. 



The flaming spark has been ascribed by some experienced observers to 

 the incandescence of the dust in the air, and especially sodium chloride. 



If the salt &c. is thus made hot, can the air in which it is mechanically 

 diffused remain cool ? 



Is not the salt &c. in the same condition as a platinum- wire held in the 

 non-luminous part of the hot burnt gas escaping from the chimney of an 

 Argand burner ? 



Will gaseous elements when combining (and in this case the nitrogen 

 and oxygen do unite, as proved by the formation of nitric acid) give a con- 

 tinuous spectrum? 



To ascertain whether the "flaming spark" could be obtained with a 

 small number of cells, the large Bunsen's battery was reduced to 3 cells ; 

 and it was found that no appreciable spark could be produced when the 

 whole primary wire was used with less than 5 cells. 



By reducing the length of the primary wire, and using the 4 divisions 

 separately, the following results were arrived at: — 



5 cells. 



inches. 



1st section, nearest core 4-J-, wiry spark. 



2nd „ 61. .. 



