xxvii.] RESULTS CONTINUED. 397" 



Iron. Iron introduced into the naked arc as metal or chloride 

 gives no reversals, but an iron rod used as positive pole reverses 

 the line 4045. By putting iron wire through the perforated 

 carbon pole into the arc of a Siemens' machine in a lime crucible, 

 the lines reversed are 4045, 4063, 4071, 4325, 4383, 4404, 4920, 

 and 4957. ' 



On adding magnesium to the lime crucible containing iron, 

 the iron lines about L and M, four strong lines below N, the line o, 

 all the strong lines from S 2 to u inclusive, and the two groups still 

 more refrangible, are reversed. 



There is an increase of continuous spectrum on adding mag- 

 nesium, just as there is on adding hydrogen. 2 



Ferro-cyanide of potassium, K 4 FeC 6 N 6 , in Siemens' arc in a lime 

 crucible gives exactly the same reversals as were produced by the 

 addition of magnesium. On passing hydrogen into the crucible, no 

 less than 140 lines were reversed. 3 



Note. Photographs taken at Kensington in 1877 clearly show 

 the reversal of 4045, 4063, and 4071 in the naked arc. 



Messrs. Liveing and Dewar have frequently expanded lines 

 without reversing them by using mixtures of metals in their 

 crucibles. ISickel alone in a magnesia crucible with the Siemens' 

 arc does not give its lines very strongly developed, but on intro- 

 ducing several other metals, such as iron, chromium, &c., the nickel 

 lines come out with great brilliance and considerably expanded, 

 remaining so for some time. 4 



An alloy of manganese, iron and titanium, had the effect of 

 making the nickel line broad and diffuse. 5 



Here the nickel molecules are to some extent protected, sufficient 

 in fact to cause the lines to expand, which is always a preliminary 

 to reversal, but since no very good shielding atmosphere like coal gas 

 or hydrogen was used, no reversals were obtained. 



The above results whenever three experiments have been made 

 under different conditions with the same metal are collected in the 

 following table : 



1 Proc. Roy. Soc. vol. xxix. p. 405. 



2 lUd. vol. xxxii. p. 403. 



3 Ibid. p. 403. 



4 Ibid. vol. xxxiii. p. 431. 

 6 Ibid. p. 434. 



