156 PROCEEDINGS COTTESWOLD CLUB 1905 
I give this as an illustration of the way, as it were, 
to correlate the horizontal record with the vertical scale 
chart. 
In practice, what is necessary for an individual is to 
compare the barometric reading and other indications, 
when the chart comes to hand, with those at 8 a.m. on the 
daily chart, and the variations indicated enable him to see 
on the chart what changes are, probably, in course of 
development, or, in other words, where he now is under 
the system prevailing when the chart was prepared. Such 
and such a depression has filled up or increased, or an 
anti-cyclone is persistent, or slowly moving in a defined 
direction. 
In considering the trace of a barograph certain refine- 
ments are possible which are of value, and should be 
noted, in making the individual forecast, which I take 
to be the object of every observer. 
If the barogram changes at a uniform rate, either up- 
wards or downwards, the resulting trace will be a straight 
line, either rising or falling, and it does not in the least 
matter how rapid the rise and fall is. If the rate of fall 
changes with diminishing pressure, the curve will become 
convex, or concave, according as the rate increases’ or 
decreases. For instance, suppose, as in the diagram, that 
the barogram fell two-tenths of an inch between one and 
two o'clock, and another two-tenths between two and three 
o'clock, the resulting trace would be a straight descending 
line like S; but if, in the second hour, the mercury fell 
three-tenths of an inch instead of two-tenths only, the 
resulting trace would be a convex like X, while if it fell 
only one-tenth in the second hour, the trace would be 
a concave as at A. 
If we define the barometric rate as the number of 
hundredths of an inch which the mercury moves, either 
up or down, per hour, the above may be put in this form. 
