LITTLE b GROUP OF LINES IN THE SOLAR SPECTRUM. 41 



deflagrating before it with condensed induction spark the several metals con- 

 cerned. My apparatus for that purpose is unfortunately very primitive and 

 weak, not more than l*5-ineh sparks in air, and 1 quart Leyden jar to condense ; 

 but by placing the spark in front of the slit, obtaining the solar spectrum 

 between the points of the sparking metals, and correcting by eye for the neces- 

 sarily curved spectral lines of 20 simple prisms, — certain definite results were 

 obtained on some of the points required, as thus — 



(1) For Magnesium. The metal spark line corresponding to ¥ is just as 

 certainly a single line, as those corresponding respectively with b 1 and b 2 ; and 

 further it falls on the second, more refrangible, and stronger component of the 

 Solar & 4 , quite suitably to its hazy physical appearance in the Sun. 



These three Magnesium spark lines moreover form an ordered triple, 

 remarkably like the Oxygen triples which I announced to the Society some 

 two years ago, in so far that the 2nd and 3rd are closer together than the 1st 

 and 2nd, and the intensities of each go on decreasing from 1st to 2nd, and from 

 2nd to 3rd, but the arrangement is on a far grander scale. 



(2) For Iron. Two of its spark lines appear in the field of view in places 

 evidently belonging to b 3 and 6 4 in a general way ; but they are both sadly 

 faint, i.e. in my weak sparking apparatus. However the stronger one is 

 remarkably sharp and may be certainly said to coincide with the first, or least 

 refrangible component of 6 4 in the Solar spectrum ; which is that one which 

 simple observation had already shown to be excentric to the characteristic 

 magnesium haze. With not by any means so much certainty, unfortunately, the 

 fainter iron line may be said to coincide with the stronger of the two recently 

 discovered components of the Solar b s . 



(3) For Nickel. Here the result was poor to utter disappointment ; the 

 tabular Nickel line concerned has only an intensity of 2 attributed to it, against 

 many that are classed as 10, by the great spectroscopists with powerful 

 apparatus ; and it appeared to me to deserve even less. Indeed I had only to 

 wander a little further on into the blue regions of the spectrum to find Nickel 

 lines there that were a pleasure and a certainty to compare with Solar lines ; 

 but the particular Nickel line in or near b 3 was so faint as to be utterly hazy and 

 undecided ; wherefore I must relegate this question of the 6 3 supposed basic line 

 to those who can produce brighter sparks of Nickel and Iron than I can. 



And there is another point touching Nickel that I would also recommend 

 to their earnest attention. Every one has heard of the Nickel line between the 

 two D lines of the Solar spectrum ; and many persons will have read in Dr 

 Marshal Watt's most useful Index of Spectra that both Thalen and 

 Kirchoff have assigned their maximum for intensity, or 10, to that Nickel 

 line. Being desirous therefore to see what such a grand line would look like in 

 the Cooke spectroscope when sparked by my apparatus, I brought it into the 



