158 



Mr. J. Norman Lockyer. 



III. Recent Photographic Investigations on the Spectra of 

 Metals at High Temperatures. 



At the time at which, the earlier inquiries to which 1 have already 

 referred were made, it was only possible for the most part to deal 

 with eye observations of the heavenly bodies. The results were, 

 therefore, limited to the visible spectrum. 



During the last few years I have been fortunate enough to 

 obtain photographs of the brighter stars and of the sun's chromo- 

 sphere during eclipses ; it became of importance, therefore, to extend 

 the observations of terrestrial spectra into the photographic regions 

 for the purpose of making the comparisons which were necessary for 

 continuing the inquiry. 



Iron. 



The facts with regard to changes in the spectrum of iron were 

 shown by my early experiments to be not much less striking than 

 those noted in the case of calcium, magnesium, and other metals. 



For the last twenty years I have devoted special attention to iron, 

 and noted many stellar and terrestrial coincidences. I shall begin 

 my account of the new work by dealing with that metal. 



Among the iron lines are two triplets, or sets of three lines, giving 

 an example of repetitions of structure in differents parts of the 

 spectrum; one of them is less refrangible than Gr, and the other 

 falls between h and H. In 1878 I wrote as follows : — 



" In many photographs in which iron has been compared with 

 other bodies, and in others, again, in which iron has been photo- 

 graphed as existing in different degrees of impurity in other bodies, 

 these triplets have been seen almost alone, and the relative intensity 

 of them as compared with the few remaining lines, is greatly 

 changed. In this these photographs resemble one I took three years 

 ago, in which a large coil and jar were employed instead of the arc. 

 In this the triplet near Gr is very marked ; the two adjacent lines 

 more refrangible near it, which are seen nearly as strong as the 

 triplet itself in some of the arc photographs I possess, are only very 

 faintly visible, while dimmer still are seen the lines of the triplet 

 between H and h. 1 '* 



It was also pointed out at the same time that the lines of iron 

 appearing in the chromosphere did not make their appearance in 

 the order of their lengths in the arc. 



For the new inquiries I have employed two storage cells giving a 

 current of 7 amperes at 8 volts, with an Apps Intensity Coil giving a 

 spark of 10 inches and a jar capacity of between 40 and 50 gallons. 



To clear the ground, it was important to determine whether the 



* ' Eoy. Soc. Proc.,' vol. 28, p. 172. 



