Royal Society. 303 



lines were more distinct when a small proportion of oxygen was ad- 

 mitted. With the full proportion of oxygen, the light from the 

 glowing erbia was more intense, but the lines were not so well seen. 

 Even with the intense heat of the oxyhydrogen flame I was unable 

 to trace the lines beyond the limits of the solid erbia, though the 

 line of sodium could be seen for some distance from the erbia. I 

 found, however, that the lines appeared more distinct, in conse- 

 quence, probably, of their being brighter relatively to the parts of 

 the continuous spectrum where they occur, when the slit was di- 

 rected from the side upon the gas immediately in front of the glow- 

 ing part of the erbia. 



The spectrum of bright lines obtained by means of the oxyhy- 

 drogen flame agreed more completely with the absorption spectrum 

 represented by Bahr and Bunsen (No. 2 in their diagram) than the 

 spectrum of bright lines figured by those observers (No. 3). The 

 most important differences occurred in the band in the red, which 

 showed two points of greatest brightness, thus forming a double line 

 with a little outstanding light, and the line in the green at 65 of the 

 scale, which was double, precisely as the corresponding absorption- 

 line is represented in spectrum No. 2 of the diagram. 



Lime. — The experiments were made with the cylinders of lime 

 prepared for use with the oxyhydrogen blowpipe, and also with 

 pieces of pure caustic lime ; but there was no sensible difference pre- 

 sented in the spectroscope. 



The bright lines consisted of a double line in the green, and 

 several bands in the orange and red, which were found to form a 

 spectrum identical with that which is produced when chloride of cal- 

 cium is heated in the flame of a Bunsen's burner. 



When the spectroscope was directed to a point in the flame a 

 little above the incandescent portion of the lime, the lines appeared 

 beyond the bright continuous spectrum, showing that they are not 

 produced by the white-hot solid lime, but by the luminous vapour 

 into which a portion of the lime has been converted by the heat of 

 the flame. 



Magnesia. — The commercial heavy oxide of magnesium was made 

 into a paste with distilled water, and formed into a small pellet upon 

 the end of a platinum wire. The pellet of magnesia was slowly dried, 

 and then placed in the oxyhydrogen flame. I was surprised to see 

 a spectrum of bright lines precisely similar to that which is produced 

 by lime. Chloride of magnesium, when introduced into the Bunsen 

 flame, gave a similar spectrum. I record these results as the oxide 

 and chloride were those sold as pure. I found afterwards that a very 

 small trace of lime may be detected in magnesia by means of the 

 oxyhydrogen flame. 



I then took metallic magnesium, which I had found by the spec- 

 troscope to be nearly pure, and formed from it magnesia and chloride 

 of magnesium. 



When this magnesia, formed into a small ball upon a wire, was 

 subjected to the oxyhydrogen flame, two bright bands were seen in 

 the green. One of these was found to be coincident with the triple 



