388 Messrs. Clayden and Heycock on the Spectra of Indium. 



On passing the spark between the metallic points another 

 spectrum is seen, consisting of sixteen lines spread over the 

 range of the luminous field: the two more-refrangible of the 

 lines shown by the chloride appear in company with fourteen 

 of lower refrangibility, while the line for which 4532 is given 

 is entirely absent. The highest line of all (4101) also suffers 

 a diminution of intensity. 



On measuring the new lines we find the following numbers, 

 giving in the first column the readings on our own scale, and 

 in the second approximately those on the scale in Dr. Watts 's 

 i Index of Spectra.' The wave-lengths are, of course, given in 

 tenth-metres ; and in the column headed Character we have 

 followed the notation of Huggins, so that n = nebulous, 

 sn = slightly nebulous, and s = sharply defined. 



Scale. 



Scale 

 (Watts). 



Wave- 

 length. 



Intensity. 



Character. 



010 



28-5 



6906 



6 



s 



755 



42-3 



6193 



10 



s 



8-65 



44-3 



6114 



2 



n 



890 



44-7 



6095 



8 



sn 



11-45 



49-3 



5922 



4 



n 



11-70 



49-7 



5905 



4 



n 



12-35 



50-9 



5862 



2 



n 



1300 



52-2 



5820 



8 



sn 



14-65 



54-8 



5722 



4 



sn 



1605 



57-3 



5644 



8 



sn 



24-40 



715 



5250 



10 



sn 



42-35 



100-7 



4680 



8 



a nd 



43-40 



1021 



4656 



8 



a nd 



4415 



103-3 



4638 



8 



band 



5005 



111-8 



4510 



10 



s 



74-70 



150-9 



4101 



8 



s 



The first line, for which 6906 is given, is very remarkable, 

 potassium, strontium, and antimony being the only elements 

 in the spectra of which any one has observed less refrangible 

 lines. The line 5250 is one of the most conspicuous, and is of 

 a bright green colour. The three which we have called bands 

 are rather broad lines, sharply defined towards the violet and 

 shading off towards the red. Their colour is bright blue. 



On experimenting with the nitrate Ave obtained a curious 

 result. The same three lines that are shown by the chloride 

 appeared; but faint indications of the presence of at least some 

 of the brighter lines of the metallic spectrum occasionally 

 flashed into sight, though all our efforts to bring them out with 

 any satisfactory clearness completely failed. We varied the 

 intensity of the spark considerably, but found the same result 

 in every case. 



