1 3 2 CONTINUO US SPECTRA. PART i. 



atmospheric air, it would betray its presence by ab- 

 sorptive bands ; nevertheless he suspects that there may 

 be some substance in the air that occasions certain 

 unaccountable changes. Possibly ozone, so intimately 

 connected with atmospheric electricity, may produce 

 some unknown effect. 



The spectra from glowing solids and liquids, such as 

 Drummond's light, which is incandescent lime, the still 

 more brilliant flame of the electric arc between charcoal 

 points, glowing solid and fused metals, and coal-gas 

 flame, are continuous; the spectra exhibit the seven 

 colours, but they are not crossed by dark rayless lines, 

 because such incandescent substances give off light of 

 all refrangibility. But solids and liquids reduced to 

 glowing vapours, and incandescent gases, only give out 

 rays of certain refrangibilities, which cross their spectra 

 at right angles, as bright lines of various colours and 

 intensities. Each glowing vapour and gas has bright 

 lines on its spectrum peculiar to itself. 



In order to compare these bright lines with Fraun- 

 hofer's dark lines, solar light is transmitted through 

 one half of the vertical slit in Kirchhoff's apparatus, 

 and the light of the luminous vapour or gas through 

 the other half. Then by prismatic refraction two 

 spectra are seen in looking through the telescope, the 

 gaseous one immediately below the solar one, and only 

 divided from it by an almost imperceptible dark line. 

 So that the bright lines appear to be continuations of 

 the dark lines if they occupy the same position in the 

 two spectra ; if not, the deviation is at once visible. The 

 coincidence or deviation of the bright lines on the 

 spectra of two volatilized substances may be determined 

 by the same method. 



The coloured light that has so beautiful an effect in 

 fire-works is owing to the combustion of the salts of 

 different metals : as soda, or common salt, which gives a 



