270 PROCEEDINGS OF SECTION A. 
that the stronger the southerly wind the stronger was the current 
setting south against it. The strength of the southerly depends: 
upon the depth of the A depression, and the lower the barometers, 
the more the southerly setting current is accelerated. The 
theoretical condition given above therefore is in exact accordance 
with the observed conditions. 
This becomes more evident if the contour of the coast lines is 
examined, for the south coast of Australia and the west coast of 
Tasmania converge into a funnel-like area, in which the wind and 
sea currents generated by the low pressure converge from opposite 
directions, and meeting in this comparatively confined area generate 
the periodic waves which are recorded on our tide-gauges at Sydney 
and Newcastle. 
We find that the lower the barometer in the A is as compared 
with Sydney the greater are the waves recorded on the tide-gauge. 
It is of importance to note here, that there may be a very low 
depression travelling along the south coast rapidly, in some cases, 
at twice the usual speed ; and when this is the case, as shown by 
many instances carefully examined, there are no periodic waves, 
such as are found when the low pressure is travelling slowly, and 
the reason appears to be, that there is not time enough for the 
ocean currents to be set in motion before the depression has 
passed by ; barometers fall and rise as usual, but the ocean is not 
sensibly affected, for water takes time to adjust itself to the varying 
atmospheric pressure. 
It is a strong confirmation of the foregoing theory to be able to 
say, after a careful examination of the records since 1867, that 62 
per cent. of the cases when periodic waves have been recorded on 
our tide-gauges, they have been coincident with the passage of 
A depressions such as I have described above. 
The probability is that a number of periodic waves are set in 
motion by storms in Tasman Sea, and of those recorded I have 
traced 1 per cent. of them to that source, which is as much as 
could be expected when we remember that in the past the logs of 
vessels crossing that sea have not been recorded. In Lake George 
T have had a self-recording anemometer and a tide-gauge at work 
since the beginning of 1885, and there, periodic waves are very 
frequently recorded, and clearly shown to be the result of violent 
gusts or squalls of wind on the lake. Lake George is about 16 
miles long (its length is affected by rain) with a depth where 
deepest of about 20 feet. On the western side there are high 
hills, and the lake is longest from north to south, so that the wind 
generally blows up or down the Jake; and sometimes a squall of 
wind will force the water to one end and make it as much as 18 
inches above its normal level. The water then flows back and 
keeps up its periodic motion, flowing backwards and forwards for 
several days, with a period of 2 hour 11 minutes, the rise and 
