300 THE CHEMISTRY OF THE SUN. [CHAP. 



at one and the same time exhibit different colours and different 

 spectra at different levels in the tube. 



It may be advantageous to dwell on the details observed 

 in the case of potassium. The tube is very perfectly ex- 

 hausted, and then gently warmed with a spirit-lamp, the 

 exhaustion going on during the whole process. On passing a 

 current between the platinum electrodes we see a beautiful 

 green glow in the tube, and obtain a certain spectrum. On re- 

 placing the spirit-lamp by a Bunsen burner we find as the result 

 of this increased temperature that the colour in the tube 

 changes to blood-red, and the spectrum is entirely different. The 

 spectrum of potassium is one which requires a very great deal 

 of study, for the reason that it varies very much under different 

 experimental conditions. If the potassium, as is well known, is 

 thrown into a Bunsen burner, the chief line that one gets is 

 a red one. Kirchhoff, in the early days of solar chemical 

 investigation, pointed out that this red line is not to be 

 found among the Fraunhofer lines. The flame also gives us 

 a line in the blue. If we examine the spectrum of potassium 

 by means of an induction-coil we find the blue line which we 

 also see in the flame, but it is intensified in the spark. We also 

 see some strong lines in the green and yellow, which are barely 

 visible in the flame which are in fact not generally recorded in 

 the flame-spectrum of potassium, although they are really visible 

 when considerable dispersion is employed. These lines in the 

 yellow and green become prominent lines. Now, it so happens 

 that some of these lines in the green do, it is believed, corre- 

 spond with Fraunhofer lines, and we are, therefore, justified in 

 assuming that they represent a something, whatever it may be, 

 in the potassium, which can withstand the heat of the sun, 

 while the red lines represent something which is broken up at 

 the temperature of those regions of which we can determine 

 the absorption. The interesting point of the experiment, 

 therefore, is this : assuming for a moment that the red line does 



