2l6 



KNOWLEDGE & SCIENTIFIC NEWS. 



[Sept., 1905. 



rotation. Some examples of these are shown in one of last 

 month's illustrations (Plate I. Fig. 3)- 



These " K " line photographs of the disc of the sun 

 will thus form the means of helping to solve many of 

 the solar riddles. Several other equally interesting 

 points to be investigated might be mentioned. 



By photographing the solar limb and the disc on the 

 same plate a means is afforded of noting the behaviour 



tion angle, neither does a flocculus passing round the 

 limb necessarily indicate the position of a large 

 prominence. In fact, it seems that although there may 

 be some relation between prominences and flocculi, it is 

 not a verv close one so far as can be judged by the few 

 photographs already discussed. 



The spectroheliograph affords a very excellent means 

 of studying the sequence of changes in the form of 



PLATE II.— Sun's Disc F'hotoxraphed in "K" (Calcium) Li>;ht. feptcmbcr 20, 1904- 



Exposed from lo h. 2S •". o ». to loh. 20 m. io>. int(r\iil 70 .sec . 

 (EnlarKcd 2! times.) 



of prominences with reference to the flocculi. Thus it 

 has been observed that although the " K " prominences 

 near the solar poles are sometimes of very great dimen- 

 sions, the mottling on the disc in these latitudes is 

 always regular and apparently undisturbed. Ag:iin, a 

 large prominence on the approaching limb of the sun 

 in lower latitudes does not always herald the presence 

 of a large flocculus region on the disc at the same posi- 



prominences. If the instrument be set up in low lati- 

 tudes where the altitude of the sun is high at noon all 

 the year round, and, consequently, the length of ex- 

 posure necessary can be reduced to a minimum, a 

 wealth of valuable information could be gleaned. In 

 these latitudes, even in summer, opportunities arc not 

 very numerous owing to the frequency of cloudy days. 

 To illustrate the nature of such photographs one 



