LOCKYER. — USE OF THE SPECTROSCOPE. 31 



bending screw should then be adjusted so that the green line of 

 the aurora is just eclipsed behind the blackened edge of the tinfoil. 

 A similar eclipse of other lines will give their positions. 



In this instrument the reference prism is brought into action 

 by turning the slipping piece to which is fixed the two terminals. 

 Care should be taken that the prism itself is adjusted before com- 

 mencing observations, as it may be shaken out of position on the 

 voyage. The tubes provided for the reference spectra may be 

 either fastened to the terminals or arranged in some other manner. 

 The air spectrum may also be used as a reference spectrum. To 

 get this two wires should be screwed into the insulators, their 

 ends being at such a distance apart and in such a position that 

 the spectrum is well seen. 



Instruments C and D. 



These being of the well-known forms require no special 

 instructions. 



General Observations regarding the Spectrum of the Aur(yra.^ 



Note appearance, colour, &c. of «rc, streamers, corona, and 

 patches of light. 



Get compass positions of principal features, and note any change 

 of magnetic intensity. If corona forms, take its position and 

 apparent height. 



Look out for phosphorescence of aurora and adjacent clouds. 

 Listen for reported sounds. Note any peculiarity of cloud scenery 

 prior to or pending the aurora. 



Sketch principal features of the display, and indicate on this 

 sketch the parts spectroscopically examined. 



Examine line in red specially in reference to its assumed con- 

 nexion with telluric lines (little a group), and note as to its 

 brightening in sympathy with any of the other li?ies. 



Examine line in yellow-green (Angstrom's) as to brightness, 

 width, and sharpness (or nebulosity) at the edges. Notice as 

 to a peculiar flickering in this line sometimes seen ; note also 

 whether this line is blighter (or the reverse) with a fall of tem- 

 perature. Note ozone papers at the time of aurora. 



Note whether the aurorae can by their spectra be classed into 

 distinct types or forms, and examine for different spectra as 

 under — 



a. The auroral glow, pure and simple. 

 /3. The white arc. 

 y. The streamers and corona. 



S. Any phosphorescent or other patches of light or light- 

 cloud in or near the aurorae. 



* In these observations some suggestions made by Mr. Capron have been 

 incorporated. 



