THE TOTAL SOLAR ECLIPSE. 107 



than at recent eclipses, the opportunity to search for new coronal bright 

 lines will be excellent. 



The accurate wave-length of the principal coronal bright line, near 

 A 5303, should be determined. A modern spectrograph, holding three 

 dense flint prisms, should make the problem easy. The accurate wave- 

 lengths of all truly coronal lines should be determined as rapidly as 

 possible, partly in order that a serious effort may be made to represent 

 them by a simple common law, as has been done for hydrogen and 

 helium. 



Of many other eclipse problems — the photometry, the shadow bands, 

 etc. — it need only be said that accurate observations will prove very 

 useful. 



The tendency of recent eclipse work is toward a unification of the 

 problem. The main divisions of the sun's structure are no longer to 

 be studied separately. Close connection has been observed between 

 spots and faculae; between photosphere and reversing layer; between 

 sun spot and coronal disturbances; between coronal streamers and 

 prominences; between prominences and chromosphere; between the 

 sunspot curve and the form of the corona; and in other ways the unity 

 of the problem is emphasized. This is only what we should expect, 

 for all these outward and visible features of the sun must be related 

 products of the stupendous forces at work within its body. In reality, 

 all observations of the sun, whether those made daily at fixed observa- 

 tories or those secured at eclipses, bear upon the solution of one prob- 

 lem : the structure, composition and condition of the sun, from its 

 center to the outermost limits of the coronal streamers. 



It is well known to eclipse observers that a regrettably large pro- 

 portion of observations of these phenomena are failures, or are but 

 partially successful. Some of these unfortunate outcomes are due to 

 nervousness at the critical moment ; a psychological state of which some 

 observers know nothing, and against which others are unable to con- 

 tend. It is a mistake to invite nervousness by attempting to do too 

 much in the limited duration of totality. If seven photographs can be 

 secured with one instrument, working with moderate speed in changing 

 plates, an attempt to secure eight by working under high nervous ten- 

 sion would be a serious error. However, the most prolific source of 

 failure is that of new instruments and new methods used for the first 

 time on eclipse day. It is not an uncommon practise to delay prepara- 

 tions until a few months or weeks before expeditions must depart for 

 their stations; to order new instruments, or new parts of instruments, 

 just in time to have them shipped from factory to station ; to use new 

 methods of focusing, etc., for the first time, at the station ; and to leave 

 insufficient time for the rehearsal of program after the instruments 

 are in supposed adjustment. It is unnecessary to say that this is cul- 



