32 LOCKYER. USE OF THE SPECTROSCOPE. 



The information collected together in the " Manual " should be 

 carefully consulted, and the line of observations suggested by Ang- 

 strom's later work followed out. To do this, not only record the 

 positions of any features you may observe in the spectrum, but 

 endeavour to determine if any, and if so which, of the features 

 vary together. Compare, for instance, the two spectra of nitrogen 

 in the Geissler tube supplied, by observing first the narrow and 

 then the wider parts of the tube. It will be seen that the dif- 

 ference in colour and spectrum results simply from an addition 

 to the spectrum in the shape of a series of channelled spaces in the 

 more refrangible end in the case of the spectrum of the narrow 

 portion. 



Try to determine whether the difference between red and green 

 auroras may arise from such a cause as this, and which class has 

 the simpler spectrum. 



See whether indications of great auroral activity are associated 

 with the widening or increased brilliancy of any of the auroral 

 lines. 



Remember that if auroral displays are due to gaseous particles 

 thrown into vibration by electric disturbance, increased electric 

 tension may either (1) dissociate those particles and thus give rise 

 to a new spectrum, the one previously observed becoming dimmer; 

 or (2) throw the particles into more intense vibration without 

 dissociation, and thus give rise to new lines, those previously 

 observed becoming brighter. 



Careful records of auroral phenomena from both ships may 

 enable the height of some observed from both to be determined. 

 It will be very important that those the heights of which are deter- 

 mined by such means should be carefully observed by the spectro- 

 scope, in order to observe whether certain characteristics of the 

 spectrum can be associated with the height of the aurora. 



VI.— MISCELLANEOUS OBSERVATIONS. 



1. On Saline Matter in Ice. By Dr. Rae, F.R.G.S. 



I find in the note-book of my visit to Repulse Bay in 1853-4 :- 

 Bay frozen over for some miles on 22nd September 1853. 



ft. in. 



20th December 1853, i ^^ ^^^^ ^^'^^"^ ] ice thick 

 ' 1 bay iroze over j 



24th January 1 854, 35 days' interval „ 



25th February „ 32 „ „ „ 



25th April „ 59 „ „ „ 



25th May „ 30 „ 



4 7 



