]\I:i.gut;tic Stparptions of Irou Lines in DiflVreut F:t.Lls. 3 



and il coinparisoii with other para-ur diaiiiagnetic elements, when 

 sufficient data are obtained, will he interesting. 



Source of Light. 



The soui-ce of hght used was the spark discharge between 25 

 percent nickel-steel terminals excited b}- an induction coil, the 

 primary circuit being fed with G amperes of alternating cun-ent of 

 110 volts, 50 cycles, obtained from the city main. 4 Leyden jars 

 were connected parallel to the spark gap directly between the 

 poles of the induction coil to obtain a condensed discharge. An 

 adjustable inductance and auxiliary spark gap with small capacity 

 were inserted in the spark circuit in series; the increase of the 

 inductance, giving the spark the character of an arc, made the 

 spectrum lines sharper and put out the air lines, with, however, a 

 considerable sacrifice in the intensity of the iron lines also; the 

 auxiliary spark gap served to control the spark under examination 

 in a favoural^le state for various magnetic fields. It is desirable 

 to ifive the spark sonorous character with steady greenish ap- 

 pearance. When the magnetic field was not strong the spark 

 continued in a favourable state for a long time, but in a strong 

 field tlie terminals soon became dark red and the spark formed 

 an arc of violet tint, making the iron lines weaker and increasing 

 the luminosity of the continuous spectrum in the back ground, 

 — this was especially remarkable in tlie green region — , so that it 

 was necessar3" to polish the tips of the terminals every 5 or 10 

 minutes. The terminals, on being polished, I'ecovered their 

 ferromagnetic property, and it was very troublesome to place 

 them in pi'oper position between the poles of the strong 

 electromagnet, which was, however, overcome l^y heating the 

 polished terminals Avith a Bunsen burner. 



Small cylinders about 1 mm. thick attached to brass reds 

 were used as terminals for most uf the experiments, and wedge 

 shaped ones were used with the strongest fields to prevent the 

 current from pa-sing through the poles of the magnet. 



