I? 



archeologist endeavoring to translate an unknown 

 language. A bilingual inscription, containing an 

 expression of the same fact in both celestial and 

 terrestrial characters, is what he requires, and this 

 a suitably equipped physical laboratory is often 

 capable of supplying. 



In the solar spectrum we can photograph about 

 20,000 lines, distributed irregularly from the red 

 to the violet, and throughout the invisible regions 

 beyond. Perhaps some of these are due to iron. 



FIG. TO. vSun-spot Spectrum, a Solar and b Spot Spectrum 

 widened; c from original negative, Spot Spectrum in middle. 



To settle this it is only necessary to vaporize some 

 iron between the poles of an electric arc and photo- 

 graph its spectrum beside that of the sun (Fig. 1 1 ). 

 Some 2,000 solar lines are found to coincide in 

 position with lines of iron. As these lines are 

 given only by iron, we may conclude at once that 

 this element exists in the solar atmosphere. 



So much for the chemical identification of lines. 

 We may next interpret their peculiarities. In the 

 case of sun-spots we suspected that certain changes 



