Epwin.—On the Principle of New Zealand Weather Forecast. 45 
detected by pressure being lowered by successive steps, none of which are 
immediately recovered. These binding-lines are an indispensable feature of 
the work, and to explain them more readily it is necessary to refer to the 
accompanying diagrams / Pl. III. ), the first of which is intended to illustrate 
the passage of a system whose low areas travel on a route inclined about 67? 
from the true North or E.N.E. It extends over a period of eleven days, an 
interval which has been, for convenience-sake, extended to fully one-third 
more time than such a system would usually occupy. Each division upon 
the line of route represents 24 hours, further subdivided into 12-hour spaces; 
and by moving the diagram on the line of route, making each division 
coincide with that upon the fixed line, and marking the barometer readings 
at Hokianga, Wellington, and Bluff upon the usual form of register, an 
illustration will be obtained of how movements, which do not appear to 
have much in common, may be shown to be the result of one system of 
depressions, and that they are in reality reciprocal.* 
This diagram shows that on the first day the barometers were 80:55 at 
Hokianga, wind north-west; 80:47 at Wellington, wind north-north-west ; 
and 80:30 at Bluff, wind north. As we advance the diagram to the right, 
we find, after an inverval of twelve hours, that it has fallen nearly a tenth at 
Hokianga, five-hundredths at Wellington, and one-tenth at the Bluff, but 
without any material change in the wind-direction, though it will have 
increased in force, and would under these circumstances amount to a 
strong wind at places in the South Island. By the second day we find 
pressure stil diminishing, and that during the last twelve hours the 
barometer has fallen to 80:40 at Hokianga, 80:80 at Wellington, and to 
90:00 at Bluff. The wind has at each of these places changed more towards 
west, backing according to meteorological law, but veering according to our 
views, and a heavy northerly gale is now blowing at places lying southward 
of the contour of 30-30, there being also a heavy north-west sea at Grey- 
mouth and Hokitika. A further interval of twelve hours shows that the 
barometer is still falling; and on the third day it reads 80:25 at Hokianga, 
wind west; 80°10 at Wellington, wind north-west; and 29-60 at Bluff 
wind about north-west. The total fall at this station now amounts to seven- 
tenths of an inch in three days, which would in reality have occurred within 
one, but it has been extended for the sake of keeping the curves further 
apart. By continuing the movement of the diagram to the right, we find 
that within the next twelve hours the barometer at Bluff makes a further 
downward movement to 29-55, giving a total decrease of seven-and-a-half 
*NorEÉ.—For the moving diagram, a chart has 1 for ko anhaa 
Lr d 3? ? 3? TP 
on which the position of New Zealand is depicted in relation to the isobaric contours af . 
successive periods of two days’ interval (Pl. III.).] —Ep. 
