316 Dr. A. Schuster on Spectra of Lightning. 



practically useless, as we can accomplish the same end in as 

 many minutes by an indirect method as it would require hours 

 by the direct method. 



The following illustration will show how it can be accom- 

 plished. The top half of the slit is covered as before, and 

 sunlight reflected onto it, and the spectrum is impressed 

 on the photographic plate. The bottom half is next covered 

 up, and a flame, in which the compound to be examined, is 

 placed in front of the slit ; the sunlight is then caused to tra- 

 verse the flame, and a second spectrum is impressed on the 

 plate through the top half of the slit. 



New absorption-lines are thus formed in the solar spectrum, 

 or those already existent are intensified, as is already well 

 known. As an example, lithium chloride was heated in the 

 flame, and the known line of lithium was found reversed be- 

 tween B and C, though absent in the spectrum of sunlight, 

 and a faint line lying in the spectrum below the red was 

 found intensified. By following out this plan we perhaps 

 may eventually establish the existence of compounds in the 

 solar photosphere. By using the light emanating from the 

 white-hot carbon points of the magnetoelectric light to produce 

 a continuous spectrum, and by burning the metallic compounds 

 as before for one spectrum, and then by using sunlight to give 

 the other spectrum, confirmatory evidence would be obtained. 

 I may remark that I have photographed brightr-line spectra of 

 lithium, and got the same line in the ultra red as that obtained 

 reversed. This method seems to promise to be a new weapon 

 of attack in solar physics, more especially in this ultra-red 

 portion. 



L. On Spectra of Lightning. 

 By Akthuk Schuster, Ph.D., F.R.A.S.* 



ALL observers of lightning-spectra agree in having seen 

 the line-spectrum of nitrogen ; but most of them have 

 seen, in addition to this, sometimes a continuous spectrum, 

 sometimes a band spectrum, the chemical origin of which 

 is unknown. 



The following historical summary may give an idea of our 

 knowledge on that point. 



Prof. Kundt (Pogg. Ann. cxxxv. p. 315) observed a line 

 spectrum consisting of one or two lines in the red, some very 

 bright ones in the green, and some less bright ones in the 

 blue. He mentions that the lines are not always seen together. 



* Communicated by the Physical Society, having been read at the 

 Meeting on February 22nd. 



