370 Mr. ,T. Kvi-i->li...l. 



" Solar Eclipse of May U8, 1900. Preliminary Report of the 

 Expedition to the South Limit of Totality to obtain Photo- 

 graphs of the Flash Spectrum in High Solar Latitudes." I'.y 

 ,T. HvKitsHKit. Head at Joint Meeting of the Iloyal and 

 1 loyal Astronomical Societies, June 28, 1900. MS. received 

 July 16, 1900. 



This expedition was one of those organised by the Joint Permanent 

 Eclipse Committee of the Royal Society and the Royal Astronomical 

 Society, funds being provided from a grant made hy the Government 

 (Jrant Committee. 



The following were the principal objects which I had in view in 

 arranging the expedition : 



To obtain a long series of photographs of the chromosphere and 

 flash spectrum, including regions of the sun's surface in mid-latitudes,, 

 and near one of the poles. 



The photographs to be obtained with a long focus prismatic camera 

 on a large scale, in order to be able to discriminate clearly between 

 high levels and low levels in the chromosphere. 



The photographs to include as much as possible of the ultra-violet 

 region of the spectrum, for the purpose of verifying the results obtained 

 with a smaller instrument in 1898, and to give more accurate values, 

 of the wave-lengths determined from those results. 



This report may be conveniently divided into the following four 

 sections, viz. : 



1. Selection of observing station. 



2. Instruments, methods of mounting, and general arrangement of 



camp. 



3. Narrative of expedition, and observations made on the day of 



the eclipse. 



4. Results. 



(1) SrltrJitw of Obterving Station. 



A consideration of the conditions under which the lowest layers of 

 the chromosphere are presented during a total solar eclipse showed 

 that a very great advantage would l>e gained by selecting a station 

 situated near the limit of the zone of total eclipse, where the two 

 internal contacts would be separated by a small angle on the sun 'a 

 limb. 



At such a station the motion of the moon relative to the sun is in a 

 direction approximating to parallelism with a tangent to the sun's 

 limb at the points of internal contact, the result being that the exces- 

 sively shallow layer giving rise to the so-ca'led " fln.sh spectrum " is. 



