THE 



WAYE-LEXdTHS 



OF 



OF THE rillNCirAL FRAUNHOFER LINES. 



OF THi: 



SOLAR SPECTlirM. 



The following pages contain the results of a serit^s of wave-length rueasnre- 

 uients male dniinij the months of Novemlicr ami Di-cemlier 1S80. It may be 

 well, in the Ix'i^inninLj. to explain why if was considered dcsirahle that these 

 measurements should be maile and the results published. 



The length of a light wave of given color has for several years ranked among 

 the ni'ist accurately determined physical constjints. In 1868 Angstrom puhlislied 

 his " litvherclies sur ie Spectre Solaire'' wdii -h contains the results of his elaborate 

 determinations of the wave-lengths of m uiy hundreds of the dark lines. This 

 work, involving as it did great labor büth iu observation and reduction, must 

 always stand among the most {wrfect of its kind an^l it is justly referred to by a 

 well known writer as "characterized by such accuracy and completeness as to 

 render it worthy of the highest admiration, t^i be regarded as a pattern to all 

 investigators." Indeed if tlie.^e residts could Im; considered strictly reliable 

 furtlier work in this direction wonki be almost unnecessary, as there are only a few 

 S|)ectroscopic researches in wldcli a greater degree of accuracy would be demanded. 



In addition to tlie work of Angstifiui numerous contriliuti.ms of wave-liMigth 

 measurements have l>een made from time to tinu- by olbcr physicists. As 

 regards measurement« of tlie dark lines of the solar spectrum, the principal uf 

 thcsr, as far as I am aware, are by l>it.scheiner, van der Willigen and Mascart. 

 Many of tlie.se me;isnrement8 ha\e been made since the publication of Angstrom's 

 work and. apparently, under eipially favonible circumstances. I5nt every student 

 of spe<troscopy is aware of the fact that tliesn me;i*inremeiits dilfer very con- 

 siderably among themselves. One only i\vM eNaininesuch a table as is given in 

 tli(! iritrfMluction to "Waltz's Inde.v of S|>eclr.i," in which variou.s mcasmementH of 

 the same lino are placed side by side, to be con\ inced that the lack of agreement 

 is »1 great, in many instances, as to throw all (d" tin- results seriously in doubt. 

 An^stiiim, in his memoir, eompire.'i the re!>nltt> obtained by Ditscheiner, van der 

 Willigen antl Ma.scHrt with hi.s own, but Ditsclieiner publislieil a revised series at 

 a later |ivriod which dilTer still more from those of Angström. 



