478 ME. A. FOWLER ON THE SPECTRUM OF MAGNESIUM HYDRIDE. 



DESCRIPTION OF PLATES. 



General Note. 



In the process of enlargement a cylindrical lens has been used to broaden the 

 spectra and smooth out irregularities produced by the grain of the gelatine films. 

 Spurious lines due to grain have been introduced in this way, but they are probably 

 too faint to appear in the reproductions. In case of doubt, comparison with the wave- 

 length catalogue may be made. 



PLATE 12. 



A. The first strip shows the three principal flutings of magnesium hydride, as photo- 

 graphed with the small Littrow spectrograph, and indicates their relative 

 intensities more correctly than the other photographs, which have been 

 copied in sections. The remaining strips give a general map of the spectrum 

 .from 5622 to 4600, as photographed in the first order of the 10-feet concave 

 grating. 



B. The photographs show the brighter parts of the green fluting, as photographed 

 with the concave grating in the second order. The principal series of lines 

 which compose the fluting are also indicated. 



PLATE 13. 



Photographs demonstrating the presence of magnesium hydride in sun-spots. The 

 photographs of the sun and sun-spot spectra were taken by Mr. EVERSHED 

 at Kodaikanal (the exposure for the sun-spot was about six times that for 

 the solar spectrum). 



The lines marked with dots in Plates 12B, and 13 are " ghosts." Other lines affected 

 by ghosts of the b group are indicated in the catalogue. 



