1902.] Discharge from Metallic Poles in Water. 



33 



and double lines which are in every respect similar to those in the spectra 

 of Nova Aurigse." Pressure, then, according to Dr. Wilsing, is the 

 cause of the duplication and broadening of the lines in the spectra of 

 new stars. 



The great importance of this result for stellar spectroscopy rendered 

 it imperative to repeat the experiments, and I at once commenced 

 them, using the large Spottiswoode coil, capable of giving a 42-inch 

 spark in air, controlled by placing a large glass plate-condenser in the 

 secondary circuit, so that a spark of length 3 mm. was obtained in air, 

 and about 0*5 mm. in water. The photographs of the more intense 

 lines in the water-spark spectrum showed very distinct reversals. 



The work was postponed a little later owing to this coil being no 

 longer available, but it was again resumed with a smaller (10-inch) coil 

 while waiting for a new large one which is under construction. 



With this coil the investigation has been extended by photographing 

 the spark spectra of several other metals in water, and these have 

 furnished material for a more general classification of the attendant 

 phenomena. 



The coil used for producing the discharge being capable of giving 

 only a 10-inch spark, had a 1 -gallon Ley den jar placed in parallel with 

 the secondary circuit. The spectrograph employed was a large concave 

 Rowland grating of 6 inches diameter, ruled with 14,438 lines to the 

 inch, and having a radius of curvature of 21 feet 6 inches. The first- 

 order spectrum was employed, arranged to photograph the region of 

 the spectrum from X 3800 to X 4800, occupying a length of 18 inches 

 on the plate. Distilled water was used in all cases. 



Of the metals so far examined (iron, silver, lead, copper, zinc, and 

 magnesium), only three — iron, zinc, and magnesium — show reversals of 

 the principal lines, and those of zinc are very weak. 



In all cases the lines of the spectrum of the spark in water are much 

 broader than the corresponding lines in the spectrum of the air-spark. 

 From an examination of the different photographs, however, showing 

 many lines of varying degrees of intensity, it appears that the 

 broadening is, for the most part, of a similar nature to that observed 

 in the arc spectrum in air when an excess of material is introduced 

 between the poles. 



The Phenomena presented by the Spark in Water, 

 (a.) General. 



In the cases of iron and magnesium, many lines undergo complete 

 reversal, for example, the following : — 



VOL. LXX. 



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