_ VOL. XV. (2) NOTES ON A DAILY WEATHER CHART — 157 
With a falling barometer the trace is convex for an in- 
creasing rate, concave for a decreasing one. A glance at 
the diagram will show that, for a rising barometer, the 
converse is the case; for when the rise is greater during 
the second than the first hour, the trace is concave as 
‘in A; but when less, then convex as at Xan this 
result may be stated as follows: with a rising barometer, 
the trace is convex for a decreasing rate, concave for 
Hours Hours 
Falling Rising 
an increasing one. This is the reverse of what happens 
with a falling barometer. Now, the simplest and com- 
monest case of barometric change occurs when the centre 
of a cyclone drifts past a station; the fall of the barometer 
is then proportional to the steepness of the gradients. 
When steeper gradients approach, the barogram will 
become convex; when slighter gradients arrive, the curve 
will be concave. The converse holds good for a rising 
barometer: when steeper gradients approach, the curve 
is concave; when slighter, then convex. 
