20 ANNIVERSARY ADDRESS. 
to me at variance with Fitzroy’s theory that they are caused by 
air-currents. A glance at the curves, plotted for a year over the 
whole Colony, shows that these waves uniformly travel from west 
to east, and in most cases so rapidly that the crest appears all over 
the Colony on the same day. Such a rapid translation seems to 
me to point to some external cause ; and on comparing Sydney 
barometer curves for 1873 with those of Greenwich for the same 
year, I was struck with the number of coincidences in the 
character of the curves. In many cases the points of elevation 
and depression occur on the same day at both places, and in 
several instances the curves follow the same form for more than 
-amonth. There are great temporary differences, due no doubt to 
‘ 
_tMany ways, and notably by Mr. Glashier, in the paper I tate 
local causes, but the similarity is very striking. 
Tt is somewhat difficult to see what could make a simultaneous 
loss of atmospheric pressure in the two hemispheres, unless it be 
the heat of the sun acting more intensely on the equator, and so 
making a great demand onthe trade winds which are supplied 
from temperate latitudes, and would, in that case, draw aff the 
pressure. The fact that such a loss of pressure causes an in-rush 
of polar wind seems to confirm this view. That there are such 
sudden changes in the sun’s heating power has been shown in 
alluded to to- — 
