1879.] On a New Method of Spectrum Observation. 



29 



Experiment No. VII. — Potassic nitrate was tried by the method pre- 

 viously described in Experiment No. I. 



The flame spectrum consisted as usual of the red lines (X 7697 and 

 7663) and the blue line (X 4045), very faint. 



The effect of the spark was to bring out the yellow lines (X about 

 5800), those in the green (X about 5340), and the red double (X 6946 

 and 6913), out of the flutings visible in the red, the double at 7697 

 and 7663 not being affected. The experiment was repeated with the 

 induction-coil, and the same observations made, with the additional 

 one that the spark also slightly intensified the blue line. 



Experiment No. VIII. — On repeating the experiment with metallic 

 potassium, the same phenomena were more markedly observed, the lines 

 ■about X 5800, and other lines more refrangible, were visible as very 

 faint objects in the flame ; they were much strengthened, however, by 

 the passage of the spark. 



Experiment No. IX. — Some potassium was volatilised by the spark 

 in front of the slit of the sun-spectroscope and comparison of the 

 positions of the lines with the Faunhofer lines made. It is believed 

 that X 5829*0, 5802*0, 5782*5 are all reversed in the solar spectrum. 

 The less refrangible member of the red double (X 6946) was next 

 compared, and was undoubtedly absent from the sun. These observa- 

 tions, however, are rendered extremely difficult on account of the 

 fluted appearance of the yellow lines, and must be repeated with a 

 stronger sun and the electric arc. The spectroscope employed had 

 three prisms, one of 60° and two of 45°. 



Experiment No. X. — The flame spectrum of magnesium was exa- 

 mined, a green triplet was observed, which was at first sight taken for 

 b. Measurements of the lines, however, showed that the less 

 refrangible member was less refrangible than 6, and had a wave- 

 length 5209*8, and that the other two members were b l and b" 

 respectively. A fresh charge of magnesium was put into the flame 

 and the spark passed ; the original triplet was now no longer visible, the 

 line at 5209*8 having vanished, but b^ was now seen forming with 

 b l and b 2 a triplet of similar form on a smaller scale. 



According to Thalen, there are three blue lines of magnesium at 

 wave-lengths 4481*0, 4586*5, and 4703*5. These lines were looked for 

 in the flame with and without the spark. Without the spark only 

 •one line was visible in this region ; its position was found by com- 

 parison with the solar spectrum to be at wave-length 4570*3, and 

 coincident with no Fraunhofer line. The passage of the spark 

 abolished this line, at the same time bringing in the two lines given by 

 Thalen at wave-length 4481*0 and 4703*5, both of which are reversed 

 in the solar spectrum. 



No line was seen at Thalen 's wave-length 4586*5, the nearest 

 approach to which was the line seen at the temperature of the Bunsen 



