on the Natiire of the Light emitted by a Substance. 227 



be raised to 35 amperes. The light used was analysed by 

 a Rowland grating, with a radius of 10 ft., and with 14,938 

 lines per inch. The first spectrum was used, and observed 

 with a micrometer eyepiece with a vertical cross- wire. An 

 accurately adjustable slit is placed near the source of light 

 under the influence of magnetism. 



3. Between the paraboloidal poles of an electromagnet, 

 the middle part of the flame from a Bunsen burner was 

 placed. A piece of asbestos impregnated with common salt 

 was put in the flame in siteh a manner that the two D-lines 

 were seen as narrow and -sharply defined lines on the dark 

 ground. The distance between the poles was about 7 mm. 

 If the current was put on, the two D-lines were distinctly 

 widened. If the current was cut off they returned to their 

 original position. The appearing and disappearing of the 

 widening was simultaneous with the putting on and off of the 

 current. The experiment could be repeated an indefinite 

 number of times. _ 



4. The flame of the Bunsen was next interchanged with 

 a flame of coal-gas fed wrth oxygen. In the same manner 

 as in § 3, asbestos soaked with common salt was introduced 

 into the flame. It ascended vertically between the poles. If 

 the current was put on again the D-lines were widened, 

 becoming perhaps three or four times their former width. 



5. With the red hues of lithium, used as carbonate, wholly 

 analogous phenomena were observed. 



6. Possibly the observed phenomenon (§§ 3, 4, 5) will be 

 regarded as nothing of any consequence. One may reason in 

 this manner : widening of the lines of the spectrum of an 

 incandescent vapour is caused by increasing the density of 

 the radiating substance and by increasing the temperature*. 

 Now, under the influence of the magnet, the outline of the 

 flame is undoubtedly changed (as is easily seen) hence the 

 temperature and possibly also the density of the vapour is 

 changed. Hence one might be inclined to account in this 

 manner for the phenomenon. 



7. Another experiment is not so easily explained. A tube 

 of porcelain, glazed inside and outside, is placed horizontally 

 between the poles with its axis perpendicular to the line 

 joining the poles. The inner diameter of the tube is 18 mm., 

 the outer one 22 mm. The length of the tube is 15 cm. 

 Caps are screwed on at each end of the tube f ; these caps 

 are closed by plates of parallel glass at one end, and are sur- 

 rounded by little water-jackets. In this manner, by means 



* Cf., however, also Pringsheini (Wied. Ann. xlv. p. 457, 1892). 

 t Pringsheim uses similar tubes in his investigation concerning the 

 adiation of gases, I. c. p. 430. 



