DISCHARGE OK KLKCTRK ri'Y. 281 



to answer very well is called the Lane-Fox pattern. When any ^as is 

 introdnced it should be sent throu.iih sulphurie acid to .^ct rid of any 

 moisture that may be in it. Owing', I tliink, to the pressure in ordin- 

 ary in('an<lesct'nt lamps being- very dittcrent from that at which the 

 discharge has its maximum ])rdliancy, 1 have nu't w itii \('r.\ i)oor suc- 

 cess in attemi)ts to i)roduce these discharges in already exhausted 

 tubes such as incandescent lamps, though 1 have tried a considerable 

 number by different makers; on the other hand, the radiometers w-hich 

 I have tried allow the discharge to pass pretty readily, though it is in- 

 terfered with by the vanes, and is not comparable in brilliancy with 

 that obtained in home-nuide tubes and bulbs. I liave obtained s])arks 

 easily with apparatus of the following dimensions: Iwo gallon Jars, the 

 outside coatings connected by a wire about 2 yards long, the coil con- 

 sisting of three or four turns, each about 3 inclies in diameter. I have 

 some bulbs which with this apparatus will give a bright discharge when 

 the distance between the terminals of the Wimshuist is only j inch; 

 these are, however, excei)tioiuUly g(»od ; it more fre(|uently takes a spark 

 an inch or an inch and a half long t(» [)roduce the discharge. 



I find that Ilittori; in Wiedenmnn's Annalen, xxi, p. 138, describes 

 the light produced in a tube round which the wire connecting the coat- 

 ings of a Leyden jar is twisted; the luminosity in Hittorf's experiments 

 seems to have filled the tube, and not, as in the experiments described 

 in this paper, been confined to a ring. It seems possible that the dif- 

 ference in the apjiearance in the tubes may have been due to the exist- 

 ence of an electrostatic action in Hittorf's experiments, the prinuiry 

 coil getting- raised to a high potential before the discharge of the jar, 

 an<l inducing a distribution of electricity over the inside of the glass 

 of the tube; on. the passage of the s])ark the potential of the primary 

 coil will tall, and the electricity on the glass re-distribute itself; to effect 

 this re-distribution itnuiy pass through the rarified gas in the discharge 

 tube and produce luminosity. 



In my experiments 1 took two precautions against this effect. In 

 the fii'st jdact^ I connected the ])riijKiry coil to earth, so that its i>oten- 

 tial befoie dischaige took place was unaltered, ami as an additional 

 precaution I sei)arated the discharge tube from the primary by a cage 

 made of blotting paper moistened with dilute acid; the wet blotting 

 ])a])er is a sufiiciently good c(mductor to screen off any i)urely electro- 

 static eifccts, but not a good enough one to intertere to an ai)preciable 

 extent with the eh'ctro-motive forces arising from ra])idly alternating 

 currents. In this way we can screen off any electrostatic effects due to 

 causes which operate before the electrical oscillations in the jars begin. 

 When once these have commenced, there ought not, I think, to beany 

 separation of the electro-motive forceps into tw^o parts, one being calh'<l 

 ele<'tro static, the other (dectro-dyiumiic. As this is a])oint on which it 

 is desirabh? to avoid an> misunderstandiug, I hope to be excused if I 

 treat it at sonu' lengtli. 



