concerning them.

I note one or two points concerning each phenomenon.

_Corona_.--White to brown inside ring called Aureola--outside
are sometimes seen two or three rings of prismatic light in
addition. Caused by diffraction of light round drops of water or ice
crystals; diameter of rings inversely proportionate to size of drops
or crystals--mixed sizes of ditto causes aureola without rings.

_Halos_.--Caused by refraction and reflection through and from ice
crystals. In this connection the hexagonal, tetrahedonal type of
crystallisation is first to be noted; then the infinite number of
forms in which this can be modified together with result of fractures:
two forms predominate, the plate and the needle; these forms falling
through air assume definite position--the plate falls horizontally
swaying to and fro, the needle turns rapidly about its longer axis,
which remains horizontal. Simpson showed excellent experiments to
illustrate; consideration of these facts and refraction of light
striking crystals clearly leads to explanation of various complicated
halo phenomena such as recorded and such as seen by us on the Great
Barrier, and draws attention to the critical refraction angles of 32 deg.
and 46 deg., the radius of inner and outer rings, the position of mock
suns, contra suns, zenith circles, &c.

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 deg. and 100 deg.--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.

Points noticed requiring confirmation:

Arch: centre of arch in magnetic meridian.

Shafts: take direction of dipping ne