Epwin.—On the Principle of New Zealand Weather Forecast. 48 
from the country. These are the special principles of New Zealand Weather 
Forecast; and the diagrams ( PI. II. ) accompanying this paper of the pressure 
within the New Zealand area on 7th, 8th, and 9th July, 1879, are examples 
drawn in aecordance with its rules, but they must not be considered specimens 
of actual forecast—a subject which will be treated of in another paper. 
In these diagrams the wind deflections are eliminated, and they are, in 
fact, diagrams of the results already arrived at. 
In support of the system now in use it may be urged that if according 
to accepted principles each cyclone, or area of low pressure, is a complete 
circle, then it follows that from whatever point pressure commenced to 
diminish it must return to that point again as the low area passes away, 
unless it be assumed that, instead of pursuing a direct route, the cyclone 
has moved in a more or less erratie course, but by this principle of 
multiple areas we can readily perceive that it is possible that gale may 
succeed gale in rapid succession, and for a considerable period, each depres- 
sion following its predecessor, and the whole system moving in a more or 
less curved but well-defined route; and it obviates what has always appeared 
to me to be an impossibility, viz.: the retrograde movement of any low area. 
Secondly: the facility with which the approach of a “ backing” wind 
can be foretold; this ‘‘backing”’ being in reality the advancing curves of 
a new depression, whose approach will cause pressure to diminish before it 
has reached the point from which it at first commenced to fall. The proxi- 
mity of such an area is shown by the extent of the area over which the 
barometer is shown to be rising, and, together with the further area over 
which the isobaric contours show that pressure is likely to increase the sea- 
movement, has also to be taken into consideration. 
Thirdly: the advantages afforded by it for reliable forecast of sea-move- 
ment, a point of information which is of considerable value to bar-harbours 
and roadsteads. 
This principle of contour lines and multiple areas enables an explanation 
to be offered as to how such complex movements, as a decrease at the ex- 
tremes and an increase in the central portions of the country, can take 
place; and, also, why several successive rapid movements may take place 
in the south without being nearly so remarkably produced in the north; 
and it also affords a means of determining the positions of the depressions, 
although they may lie at a considerable distance to seaward. 
It also shows the existence of what may be termed double-centred areas 
of low pressure ; in these the barometer falls rapidly, the wind veering by 
north and west and blowing a heavy gale, a recovery then sets in, the wind 
changes southward of west, and the barometer rises rapidly for about half 
an inch, and immediately that it reaches its highest point it commences to 
