KENT. — THE SPECTRA OF TITANIUM, ZINC, AND IRON. 285 



opeuing (4 cm. in diameter) being about 2 cm. distant from the spark. 

 When a secondary spark was used in series with that under investigation, 

 the side draft from the fan was allowed to play upon it also. The fan 

 undoubtedly produces greater disruptiveness and increases the potential 

 of the discharge ; but its steadying influence is very desirable, especially 

 when self-induction is used in the discharge circuit. The luminous imago 

 was tunned on the slit by a glass lens (aperture 3 inches, focal length 

 25 inches, made by Bausch & Lomb) situated about 110 cm. from the 

 source of light and 152 cm. from the slit. This lens was held in a metal 



TABLE II. 



Dimensions of Self-Induction Coil in cm. Gauge Number of 

 WiRE = li s.w.g. External Diameter = 0.54. cm. 



casing clamped to a marble slab which was set on an iron pipe imbedded 

 in a cement foundation. 



In all cases the spark which was being photographed was placed in a 

 horizontal position in view of the possibility that different regions of the 

 spark might show different spectra. 



In the primary circuit of the transformer were placed a Thomson in- 

 dicating watt-meter (maximum voltage 150 volts, maximum current 50 

 amperes, graduated in hectowatts) and a Thomson alternating ammeter 

 (maximum current 100 amperes). The primary voltage was read by a 

 Weston direct reading, alternating and direct current, voltmeter (two 

 scale instrument, 15 and 7-J volts, 1 to 10 multiplier). 



The arc was developed by a 133 cycle alternating circuit, the current 

 used being about 1 2 amperes, measured by a 50-ampere Aryton and 

 Perry spring ammeter. The discharge took place between one-half inch 

 carbons, the lower one of which was of the cored type and was hollowed 

 out a trifle to receive the small pieces of metal used. The distance 

 between the terminals was always in the neighborhood of 3 mm. That 

 the energy for the spark and arc discharges could be obtained from the 

 city circuit was a distinct advantage, for during the exposures there were 



