408 [Jan. 15, 



Portions of metallic thallium, as well as of an alloy formed by 

 fusing a bead of thallium upon the end of a platinum wire, and por- 

 tions of the sulphate of the metal were introduced successively, 

 first, into the flame of burning hydrogen, and then into the oxyhy- 

 drogen jet, and were in each case viewed by the spectroscope. As 

 the temperature increased in intensity, the brilliancy of the thallium 

 green line increased also, but no new lines made their appearance. 



Two pieces of stout thallium wire were then arranged as electrodes 

 to the secondary wire of an induction coil. A continuous torrent of 

 sparks was maintained without melting the wires or producing very 

 rapid oxidation, or volatilization of the metal ; the light, however, 

 was much whiter than its ordinary monochromatic character would 

 have led us to expect. Mr. Crookes, who was with me during the 

 experiments, projected the image of the points by means of a lens 

 upon a distant white screen, when it was at once obvious that 

 the extremities of the spark were of a fine green colour, whilst the 

 flickering luminous arc, which filled up the interval, due chiefly to 

 ignited air, was much whiter. 



On viewing the sparks from the induction-coil by the spectroscope, 

 several new lines, independently of well-marked air-lines, made their 

 appearance. These lines were distinguished from air-lines by the 

 peculiar character which distinguishes most metallic lines, viz. the 

 much greater intensity of their extremities than of their central por- 

 tions. Besides the usual intense line in the green, five others were 

 particularly observable : first, a very faint one in the orange ; next, 

 two of nearly equal intensity in the green, more refrangible than Tla, 

 with a third much fainter, these three lines in the green being nearly 

 equidistant; whilst, 5th, in the blue was a bright well- defined line : 

 all these were strong at each extremity and evanescent in the central 

 portions. 



The induction-spark of thallium was then observed when produced 

 in a current of hydrogen gas. The air-lines disappeared, the pecu- 

 liar lines of hydrogen were very manifest, particularly the line in 

 the red and one of the lines in the blue ; whilst the new thallium 

 lines were preserved, with the exception of the feeblest, though all 

 were reduced in intensity. 



Finally, a photographic impression of the thallium spectrum upon 

 collodion was obtained by the method which I have described in a 



