Further measurements are needed; for instance of streamers from mock suns and examination of ice crystals. (Record of ice crystals seen on Barrier Surface.)
_Rainbows_.--Caused by reflection and refraction from and through _drops of water_--colours vary with size of drops, the smaller the drop the lighter the colours and nearer to the violet end of the spectrum--hence white rainbow as seen on the Barrier, very small drops.
Double Bows--diameters must be 84° and 100°--again from laws of refraction--colours: inner, red outside; outer, red inside--i.e. reds come together.
Wanted to see more rainbows on Barrier. In this connection a good rainbow was seen to N.W. in February from winter quarters. Reports should note colours and relative width of bands of colour.
_Iridescent Clouds_.--Not yet understood; observations required, especially angular distance from the sun.
_Auroras_.--Clearly most frequent and intense in years of maximum sun spots; this argues connection with the sun.
Arch: centre of arch in magnetic meridian.
Shafts: take direction of dipping needle.
Bands and Curtains with convolutions--not understood.
Notes required on movement and direction of movement--colours seen--supposed red and possibly green rays preceding or accompanying movement. Auroras are sometimes accompanied by magnetic storms, but not always, and vice versa--in general significant signs of some connection--possible common dependents on a third factor. The phenomenon further connects itself in form with lines of magnetic force about the earth.
(Curious apparent connection between spectrum of aurora and that of a heavy gas, 'argon.' May be coincidence.)
_Arrhenius_.--Bombardments of minute charged particles from the sun gathered into the magnetic field of the earth.
_Birkeland_.--Bombardment of free negative electrons gathered into the magnetic field of the earth.
It is experimentally shown that minute drops of water are deflected by light.
It is experimentally shown that ions are given off by dried calcium, which the sun contains.
Professor Störmer has collected much material showing connection of the phenomenon with lines of magnetic force.
_Thursday, May_ 4.--From the small height of Wind Vane Hill (64 feet) it was impossible to say if the ice in the Strait had been out after yesterday's wind. The sea was frozen, but after twelve hours' calm it would be in any case. The dark appearance of the ice is noticeable, but this has been the case of late since the light is poor; little snow has fallen or drifted and the ice flowers are very sparse and scattered.