( 277 ) 



The aiijilomy between lliese altiioriiuil a|)|)earaiices and lliosc» of (lie 

 ypeetruiii of Half, is ohxious. riitortiuuilely the part of the spectriiin 

 investij^ated hv Lockvku (exteiidinu' fr(»inP.48H3 to P. 5(SJ)3) lies entirely 

 ontside the part [)holo<iraphed l»_v Halk (a .'US 12 — P. 4J32) whieh 

 renders direct comparison impossible, hiil the parallelism to whieh 

 we pointed, makes us anticipate that also in the aspect of the average 

 photosphere spectrum, as well as in the s|)ot s|)ectrum, the ll-year 

 period will be fonnd. 



LocKYER holds that in years of spot maximum the Sun's activity is 

 greatly increased; that the more \iolent eruptions then cansc a 

 considerable rise in its temperature. To this tact he ascribes the 

 appearance of "unknown lines" and the weakening of the known 

 lines, on the same principle as that which governs the variations 

 produced in the emission spectra when |)assing from the arc to the 

 induction spark ^). 



On the othei' hand Cn. Nordmann ') has j)ublished the results of 

 an exhanstive inqniry into the variations of the temperature all over 

 the Earth, between the years J 870 and 1900. From his statements 

 it appears that the mean temj)erature nndergoes indeed a periodical 

 variation coinciding with the sun-s})Ot j)eriod, but in this maimer, 

 that the maxima of the curve of spot frequeiRw coi-respond to the 

 minima of the temperatui-e curve. This result seenis to us a serious 

 objectioii to the views of Lockvkk. 



We will now see if by applying our tli(>ory, based on the disper- 

 sion of light, it is possible to find a consistent exitlanation for the 

 results l)oth of Lockykr and NoRD.ArANN. 



To Hs the peculiarities of Lockykr's spot sjtectruni are phenomena 

 of the same nature as those obser\ed in the abnormal s[)ectrnni 

 described b}' Hale. We have found an explanation foi- the latter by 

 supposing that just at the time when the j)hotogiaph was taken, 

 a long corona sti'eamer was directed to the Earth, so that the line 

 of sight almost coincided with the tangent af a sui'tace of discon- 

 tinuity. The visible structure of the corona with its long, almost 

 straight lines, is to us an indication that the light of the 8nn, accor- 

 ding to the position occupied by the Eai'tli, must at one time reach 

 US alon^' sharply delined surfaces of discontinuity and at othei'S not. 

 Provisionally neglecting possible variations in the distribution of 

 matter which might take |)lace in the Sun itself, the condition for 

 each successive moment will be accurately defined by the place 



1) LocKYER, Proc. Roy. Soc. 07, p. 411— i J (i, (11)00). 

 ") Gh. Nürdm.\nn, G. R. 136, p. 1047 — lü5U, (l'JO:jj. 



19 

 Proceedings Royal A.cad. Anislerdam. Vol. VI, 



