868 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
that part of the Barrier had been equal to about 7.5 inches of rain 
per year. If it is assumed that the rate of accumulation of solid 
snow over the Barrier is 12 inches of consolidated snow per year, 
then it follows, since the Barrier extends south for about 300 miles, 
and is moving northward at the rate of about one-third of a mile 
per year, that a layer of snow deposited 300 miles inland will be cov- 
ered by a depth of 900 feet of snow when it reaches the Barrier edge 
nine hundred years later. This theory suggests that the Barrier is 
an accumulation of snow rather than of glacier ice, and was sup- 
ported by the evidence of bergs which were examined by the expedi- 
tion. ‘The typical antarctic berg is formed of consolidated snow. 
The question of what becomes of the ice from the inland glaciers 
remains unanswered. The Barrier is certainly afloat at its northern 
edge, and perhaps the ice, weighed down by superimposed snow, is 
thawed away by the sea water. Some true icebergs are found in the 
Antarctic. 
The expedition made a special study of meteorological optics, and 
some very interesting observations were made, and will be dealt with 
by the scientific members in the memoirs. The curious “ earth 
shadows ” were observed in a variety of forms. Some of them seemed 
clearly to have a relation to the relative positions of Mount Erebus 
and the sun. Other forms were not so easily explained. In the 
spring, when the sun was low in the northern sky, we saw above us 
six parallel earth-shadow beams, directed from the sun. 
The scientific memoirs of the expedition will deal in detail with 
geology, biology, meteorology, magnetism, physics, chemistry, and 
mineralogy, tides and currents, optics, and other scientific subjects. 
We were a small party, and of necessity a considerable part of our 
time was occupied in the necessary routine duties incidental to daily 
life in the Antarctic, but we tried to cover all the ground possible in 
the various branches of scientific knowledge. It is probable that 
most of the volumes containing our scientific records and conclusions 
will be published within the next twelve or eighteen months. 
The last stage of the expedition was a search by the WVimrod for 
some of the charted southern islands the existence of which is doubt- 
ful. The ship sailed over the positions assigned to the Royal Com- 
pany Island, Emerald Island, the Nimrod Islands, and Dougherty 
Islands, without having sighted land. 
