448 Bev. Walter Sidgreaves on Astrophysical Problems, [Jan. 22, 



the 15-hour interval ; for it should be remembered that the plates 

 must be of different civil dates, in order to eliminate variations 

 dependent on atmospheric conditions, and consequently the plates 

 must be exposed in different light cycles. It might be very long 

 before one succeeded in acquiring a dozen plates within any one 

 24-hour interval of a cycle. 



The hour is nearly ended, and I promised myself not to exceed 

 it. It is, therefore, with some regret that I must leave my subject 

 unfinished. It would have been a satisfaction to have laid the whole 

 case of /5 Lyrae before you, as it has come before me in my spectro- 

 scopic study of its problems. I must not, however, leave unanswered a 

 question which I imagine you are mentally asking : What do I con- 

 sider truly demonstrated ? My answer is simple : Only this, that 

 the method of studying the variable spectrum of /3 LyrsB, as I have 

 illustrated this evening, is full of promise, and worthy of being 

 carried out with a telespectrograph more capable than mine of 

 writing with accuracy the history of a star which has been rightly 

 named by Miss Gierke the " Problem Star." 



[W. S.] 



WEEKLY EVENING MEETING, 

 Friday, January 29, 1904. 



Sir James Crichton Browne, M.D. LL.D. F.Ii.S., Treasurer 

 and Vice-President, in the Chair. 



David George Hogarth, Esq., M.A. 



The Marshes of the Nile Delta. 

 [abstract.] 



There is a part of Egypt never visited by tourists, but not without 

 considerable interest owing to the singularity of both its conforma- 

 tion and its population. This is the seaward belt of the central 

 Delta. The southern part of this belt has few inhabitants except those 

 of recent origin, mostly derived from refugees who migrated thither 

 during the 18th and early 19th centuries ; but there are abundant 

 traces of a large ancient population, and it was to study these traces 

 that the lecturer visited the locality in the spring of 1903. 



Leaving the Berari railway one soon passes northward beyond the 

 margin of cultivation and the last mud-hamlets, built in fantastic 

 pepper-pot forms, on to great salt flats singularly devoid of all 

 life, and rendered treacherous by the overflowing of old drains and 



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