EFFECT OF PRESSURE UPON ARC SPECTRA. NICKEL. 



TABLE I. 



207 



10 atmospheres 

 20 



10 atmospheres 



20 



40 (2) 



60 (2) 



10 atmospheres 

 20 



10 atmospheres 



X = 3450 to X = 4050. 



40 atmospheres 

 60 



X = 4050 to X = 4600. 



70 atmospheres 



80 



93 



X = 4600 to X = 5120. 



40 atmospheres 

 60 



X = 5120 to X = 5500. 

 20 atmospheres 



80 atmospheres 

 100 



110 atmospheres 



155 



200 



80 atmospheres 

 100 



75 atmospheres 



The plates used were Imperial Flashlight and the developer Imperial Pyro-Metol 

 Standard. The exposure varied from five minutes to one hour according to the region 

 examined, and the difficulty with which the arc burned. It should be noted that 

 one hour is the total time expended upon the exposure, and includes the time when the 

 arc was being re-struck. The total time during which the arc burned is a small 

 fraction of this as a rule. The effect upon the photographic plate is that of the sum 

 of a very large number of short-lived arcs. 



(2) Description of the Plates. Plates 1 to 5 illustrate the behaviour of the Nickel 

 Arc under different pressures. Plate 1 includes the region X = 3450 to X = 3740, 

 Plate 2 the region X = 3740 to X = 4050, Plate 3 the region X = 4030 to X = 4350, 

 Plate 4 the region X = 4350 to X = 4610, and Plate 5 the region X = 4600 to X = 4900. 

 The photographs are full-size positive reproductions of the originals, and are arranged 

 in order of increasing pressure from the top at one atmosphere to the bottom at -1- 100 

 or +200 atmospheres. The arbitrary numbers enumerated in Table III. have been 

 affixed to facilitate reference to them. 



The central strip in each photograph is the spectrum at atmospheric pressure, and 

 corresponds to the spectrum at the head of each Plate. Above and below this strip 

 are the lines as they appear when the arc is subjected to pressure. The central strip 

 was taken partly before and partly after the pressure exposure, and this provides 

 a check upon the value of each photographic plate. The shutter which made this 



2 E 2 



