Graphics Reference
In-Depth Information
Figure . . [his figure also appears in the color insert.] Mosaic plots for milestones items, classified by
Subject, Aspect and Epoch. Cells with greater (less) frequency than expected under independence are
coloured blue (red), with intensity proportional to the deviation from independence
detailed definitions than described here;however, it seems reasonable tosuggest that
such analyses of history as 'data' are a promising direction for future work.
What Was He Thinking? -
Understanding Through Reproduction
1.3.3
Historical graphs werecreated using available data, methods, technology and under-
standing current at the time. We can oten come to a better understanding of intel-
lectual, scientific and graphical questions by attempting a re-analysis froma modern
perspective.
Earlier, we showed Playfair's time-series graph (Fig. . ) of wages and prices and
notedthatPlayfairwishedtoshowthatworkerswerebetteroffattheendoftheperiod
shown than at any earlier time. Presumably he wished to draw the reader's eye to the
narrowing of the gap between the bars for prices and the line graph for wages. Is this
what you see?
What this graph shows directly is quite different from Playfair's intention. It ap-
pears that wages remained relatively stable while the price of wheat varied greatly.
heinference that wagesincreased relative toprices is indirect and not visually com-
pelling.
Wecannot resist thetemptation togive Playfairahelpinghandhere-bygraphing
theratioofwagestoprices(labourcostofwheat),asshowninFig. . .Butthiswould
not have occurred to Playfair because the idea of relating one time series to another
by ratios (index numbers) would not occur for another half-century (due to Jevons).
See Friendly and Denis ( ) for further discussion of Playfair's thinking.
As another example, we give a brief account of an attempt to explore Galton's
discovery of regression and the elliptical contours of the bivariate normal surface,
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