356 



Profs. Liveing and Dewar 



[Feb. 20, 



catch the smoke, which would otherwise soon dim the surface of the 

 mirror. 



Fig. 2. 



With the jet of coal-gas and oxygen the usual green and orange 

 bands of lime and the violet line of calcium (wave-length 4,226) were 

 seen bright on the continuous spectrum, and on dropping in some 

 aluminium their brightness increased at the same time that a dark 

 line appeared in the middle of both the orange and green band. This 

 dark line speedily disappeared in the case of the orange band, but 

 lasted longer in the green band. When some lithium carbonate was 

 put into the crucible and the coal-gas turned on so as to be in excess,, 

 the red lithium line was reversed, appearing slightly expanded with 

 a black line down the middle. 



For the electric arc 25 Grove's cells were used, and the carbon 

 poles introduced through the lateral openings, so as to meet at the 

 bottom of the vertical boring of the lime crucible. A very brilliant 

 spectrum of bright lines was produced on bringing the poles in con- 

 tact, while a copious stream of vapours ascended the tube. On 

 drawing apart the poles, which could be done for nearly an inch 

 without stopping the current, the calcium line (wave-length 4,226) 

 was seen reversed. On dropping some aluminium into the crucible 

 the calcium line just mentioned was very much expanded, and 

 appeared with a broad black line in the middle. The other calcium 

 lines in the neighbourhood on the less refrangible side were also ex- 

 panded considerably, but were not seen reversed. The more refran- 

 gible lines (Fraunhofer's H), however, remained sharply defined, and 

 did not appear sensibly expanded or reversed. 



On introducing some strontia the blue strontium line (wave-length 

 4,607) was immediately seen reversed, appearing as a broadish bright 

 band, with a dark line in the middle. There were no indications of 

 the reversal of any other strontium line, though, the more refrangible- 

 lines were conspicuously bright. 



