A NEW METHOD OF RESEAIK II. 



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study of the spectrum of various portions of the sun's surface had 

 shown the existence at many points of great regions of calcium vapor, 

 luminous enough to render their existence evident through the pro- 

 duction of bright II and K lines on the solar disk (Fig. 1, b and c). 

 Some of these calcium regions had indeed been known to exist through 

 the visual observations of Professor Young, who had observed the 

 bright lines in the vicinity of sun-spots. But the vast extent of the 

 calcium regions, and the characteristic forms of the phenomena, could 

 not be ascertained by such means. What was required was such a 



Fig. 4. Ordinary Photograph of the Sin. 



representation of the solar disk as the spectroheliograph had been de- 

 signed to give in the case of the prominences. From a consideration 

 of the results obtained in the spectroscopic study of the disk, it ap- 

 peared probable that an important application of the spectroheliograph 

 might be made in this new direction. 



Before describing this second application of the instrument, it may 

 be well to call attention to the appearance of the sun when seen with 

 a telescope, or when photographed in the ordinary manner, without a 



