DISRUPTIVE DISCHARGE — DARK DISCHARGE IN DIFFERENT GASES. 141 



and flamy, like a very exhausted and sudden, but not a dense sharp spark ; and with 

 a still larger interval, produced a feeble brush on the inductric positive end, and a 

 glow on the inducteous negative end, the dark part being between (1544.); and at 

 such times, the spark at the conductor, instead of being sudden and sonorous, was 

 dull and quiet (334.). 



1555. On introducing more muriatic acid gas, until the pressure was 29*97 inches, 

 the same terminations gave bright sparks within at small distances ; but when they 

 were about an inch or more apart, the discharge was generally with very small brushes 

 and glow, and frequently with no light at all, though electricity had passed through 

 the gas. Whenever the bright spark did pass through the muriatic acid gas at this 

 pressure, it was bright throughout, presenting no dark or dull space. 



1556. In coal gas, at common pressures, when the distance was about an inch, the 

 discharge was accompanied by short brushes on the ends, and a dark interval of half 

 an inch or more between them, notwithstanding the discharge had the sharp quick 

 sound of a dull spark, and could not have depended in the dark part on convection. 



1557. This gas presents several curious points in relation to the bright and dark 

 parts of spark discharge. When bright sparks passed between the rod ends 0*3 of 

 an inch in diameter (1544.), very sudden dark parts would occur next to the brightest 

 portions of the spark. Again, with these ends and also with balls (1422.), the 

 bright sparks would be sometimes red, sometimes green, and occasionally green and 

 red in different parts of the same spark. Again, in the experiments described (1518.), 

 at certain intervals a very peculiar pale, dull, yet sudden discharge would pass, which, 

 though apparently weak, was very direct in its course, and accompanied by a sharp 

 snapping noise, as if quick in its occurrence. 



1558. Hydrogen frequently gave peculiar sparks, one part being bright red, whilst 

 the other was a dull pale gray, or else the whole spark was dull and peculiar. 



1 559. Nitrogen presented a very remarkable discharge, between two balls of the re- 

 spective diameters of 0*15 and 2 inches (1506. 1518.), the smaller one being rendered 

 negative either directly or inducteously. The peculiar discharge occurred at intervals 

 between 0*42 and 0*68, and even at 1*4 inches when the large ball was inductric po- 

 sitively ; it consisted of a little brushy part on the small negative ball, then a dark 

 space, and lastly a dull straight line on the large positive ball (fig. 20.). The position 

 of the dark space was very constant, and is probably in direct relation to the dark 

 space described when negative glow was produced (1544.). When by any circum- 

 stance a bright spark was determined, the contrast with the peculiar spark described 

 was very striking; for it always had a faint purple part, but the place of this part was 

 constantly near the positive ball. 



1560. Thus dark discharge appears to be decidedly established. But its establish- 

 ment is accompanied by proofs that it occurs in different degrees and modes in different 

 gases. Hence then another specific action, added to the many (1296. 1398. 1399. 

 1423. 1454. 1503.) by which the electrical relations of insulating dielectrics are distin- 



