To-day have had our first game of football; a harassing southerly wind sprang up, which helped my own side to the extent of three goals.
This same wind came with a clear sky and jumped up and down in force throughout the afternoon, but has died away to-night. In the afternoon I saw an ominous lead outside the Island which appeared to extend a long way south. I'm much afraid it may go across our pony track from Hut Point. I am getting anxious to have the hut party back, and begin to wonder if the ice to the south will ever hold in permanently now that the Glacier Tongue has gone.
Wednesday, May 3.—Another calm day, very beautiful and clear. Wilson and Bowers took our few dogs for a run in a sledge. Walked myself out over ice in North Bay—there are a good many cracks and pressures with varying thickness of ice, showing how tide and wind shift the thin sheets—the newest leads held young ice of 4 inches.
The temperature remains high, the lowest yesterday -13°; it should be much lower with such calm weather and clear skies. A strange fact is now very commonly noticed: in calm weather there is usually a difference of 4° or 5° between the temperature at the hut and that on Wind Vane Hill (64 feet), the latter being the higher. This shows an inverted temperature.
As I returned from my walk the southern sky seemed to grow darker, and later stratus cloud was undoubtedly spreading up from that direction—this at about 5 P.M. About 7 a moderate north wind sprang up. This seemed to indicate a southerly blow, and at about 9 the wind shifted to that quarter and blew gustily, 25 to 35 m.p.h. One cannot see the result on the Strait, but I fear it means that the ice has gone out again in places. The wind dropped as suddenly as it had arisen soon after midnight.
In the evening Simpson gave us his first meteorological lecture—the subject, 'Coronas, Halos, Rainbows, and Auroras.' He has a remarkable power of exposition and taught me more of these phenomena in the hour than I had learnt by all previous interested inquiries 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° and 46°, 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.)