Graphics Reference
In-Depth Information
Galtons Contributions
Specialnoteshouldbemadeofthevariedcontributions ofFrancisGalton[ - ]
to data visualization and statistical graphics. Galton's role in the development of the
ideas of correlation and regression are well known. Less well known is the role that
visualization and graphing played in his contributions and discoveries.
Galton's statistical insight (Galton, ) - that, in a bivariate (normal) distribu-
tion, (say, height of a child against height of parents), (a) he isolines of equal fre-
quencywouldappearasconcentric ellipsesand(b)helocusofthe(regression)lines
of means of y
y were the conjugate diameters of these ellipses - was based
largely on visual analysis fromthe application of smoothing to his data. Karl Pearson
would later say 'that Galton should have evolved all this from his observations is to
my mind one of the most noteworthy scientific discoveries arising from pure analy-
sis of observations.' (Pearson, , p. ). his was only one of Galton's discoveries
based on graphical methods.
In earlier work, Galton had made wide use of isolines, contour diagrams and
smoothing in a variety of areas. An paper showed the use of 'isodic curves' to
portray the joint effects of wind and current on the distance ships at sea could travel
in any direction. An 'isochronic chart' (Galton, ) showed the time it took
to reach any destination in the world from London by means of coloured regions
on a world map. Still later, he analysed rates of fertility in marriages in relation to
the ages of father and mother using 'isogens,' curves of equal percentage of families
having a child (Galton, ).
But perhaps the most notable non-statistical graphical discovery was that of the
“anti-cyclonic” (anticlockwise) pattern of winds around low-pressure regions, com-
binedwithclockwiserotationsaroundhigh-pressurezones.Galton'sworkonweather
patterns began in and was summarized in Meteorographica ( ). It contained
a variety of ingenious graphs and maps (over illustrations in total), one of which
is shown in Fig. . . his remarkable chart, one of a two-page Trellis-style display,
shows observations on barometric pressure, wind direction, rain and temperature
from days in December . For each day, the
x and of x
grid shows schematic maps
of Europe, mapping pressure (row ), wind and rain (row ) and temperature (row
), in the morning, aternoon and evening (columns). One can clearly see the series
of black areas (low pressure) on the barometric charts for about the first half of the
month, corresponding to the anticlockwise arrows in the wind charts, followed by
a shit to red areas (high pressure) and more clockwise arrows. Wainer ( , p. )
remarks, 'Galton did for the collectors of weather data what Kepler did for Tycho
Brahe. his is no small accomplishment.'
Statistical Atlases
he collection, organization and dissemination of o cial government statistics on
population, trade and commerce, social, moral and political issues became wide-
In July , Galton distributed a circular tometerologists throughout Europe,asking them
torecordthesedata synchonously,threetimesadayfor theentiremonthofDecember .
About weather stations supplied the data; see Pearson ( - , pp. - ).
Search WWH ::




Custom Search