492 Mr. De La Bue on Electric Discharge. [Jan. 21, 



PAGE 



Lightning, potential necessary to produce a flash of, a mile long .. .. 470 

 Current necessary to produce a powerful flash of, according to Faraday 464 



Micrometer-Discharger 469 



Microscope with revolving mirror used to show intermittence in a 



discharge 478,479 



IMoLECULES, the relative number of, in a given linear space at various 



pressures 473 



Polarisation, non-existence of, in the terminals of vacuum tubes .. .. 474 



Pulsation of Current in a vacuum tube even when strata are perfectly 



steady 479-481 



Rapid Current-Reverser used in certain cases 487 



Resistance to a discharge in gases diminishes with the pressure up to a 

 certain point of minimum resistance^ then increases as the pressure 

 is diminished 473,474 



Rheostat, Gaston-Plante's, or cascade, increase of length of spark by its 



use 470,471 



Sensitiveness of discharge in a vacuum tube to external influences . . 488 



Spottiswoode tube with shifting terminal 483, 484 



Strata in a vacuum tube resemble drops of water from a jet 465 



They recall the Lycopodium records of sound pulsations .. .. 485 



Usually a dark space towards negative beyond strata 487 



But in some cases strata reach right up to and thread themselves 



on the negative terminal 487 



Rapid alteration produced in phases of, by an oft-repeated current 487, 489 



Tyndall — Resolution of jet of water into drops, shown at his lectures .. 465 

 Stratified records of sound pulsations 485 



Vacuum Tubes, discharge in, is a magnified arc 467 



A high exhaust does not permit a discharge to take place in them . . 474 

 Plate^of, references to text : 



Fig. i, 2, tube 163, with two branches 488 



488 



with double strata 487 



double-tongued strata 488 



cross strata 488 



close strata 487 



luminous entities 487 



icid shifting terminal 485 



steady blocks of light 480 



of large dimensions illustrating 



aurora 475 



