KENT. — SPECTRA OF THE ZINC ARC AND SPARK. 103 



4680 in the double order condition showed the fluting faintly at 

 times, while with inductance the line appeared almost single, the 

 ^'reversal" being almost invisible. 



This visual work with the spark shows : — 



(1) That at high inductance 4810 and 4680 are generally double; 

 (4810 has been photographed as quadruple, and, ivith less inductance, 

 as a quintuplet and a triplet) and 4722 triple. 



(2) That here we have a definite asymmetry, controllable and regu- 

 lar, a relative increase in intensity of the red satellites when the end 

 of the spark gap is used. This is fully confirmed by the photographic 

 study. (See discussion below and Plate 1, 71 (a), (c), and 111 (b).) 



Photographic stuby of arc and spark lines and a comparison 

 OF the two. ^° Among others the following photographs were taken 

 with the Porter echelon: — 



The "fluting'' not visible in all disruptive spark lines. 



12. 4722. Spark without inductance. Center of 4 mm. gap. 

 Shows fluting. 



16. Zri4924. Without inductance. Center of 4 mm. gap. Shows 

 no fluting. This may be an "air" line, however. 



The following photographs were taken with the Petitdidier echelon : 



A general comparison of the images of a line as given by different 

 sources. 



28. 4810. Pfund arc through two of the openings of the five open- 

 ing shutter; spark through three openings. Arc current, 0.9 amp. 

 Spark without inductance. Gap 2 mm. and in series an auxiliary gap 

 of 4 mm. Exposures: arc 20 seconds, spark 2 minutes. Compares 

 the pattern and position of arc and spark images, under the double 

 order condition. Confirmed by other similar photographs. However, 

 we cannot tell with the echelon a disruptive spark from an arc burning 

 on a heavy current, as is shown by 36. 



32. 4680. Similar to 28. Compares the arc and spark images 

 under single order condition. Confirmed by other similar photo- 

 graphs. 



36. 4810. Inside 110 volt arc of about 10 amp. between Pfund 

 terminals and very dense vapor. Outside Pfund arc, 1 amp. Com- 

 pare 28. 



52. 4810. Center of 4 mm. gap of disruptive spark, inside open- 

 ing of three opening shutter; Nernst lamp (in neighborhood of 4810), 

 outside openings. Exposures: Nernst, 1 minute; spark, 15 seconds. 

 Shows that the two cannot be distinguished. 



20 For the photographs which have been reproduced see Plates 1 and 2. 



