The existence of this weekly rhythm
being granted, it would naturally be assumed that either the maximum or
the minimum would regularly occur on Saturday or Sunday; but an
examination of the curves discloses the unexpected result that the day of
maximum discharge varies from year to year. Thus it is[383]
Sunday in 1888, 1892, 1896.
Tuesday in 1894.
Thursday in 1886, 1897.
Friday in 1887.
Saturday in 1893 and 1895.
Since, in Chart 11, the curves are drawn from Sunday to Sunday, it is
obvious that the real symmetry of the curve is brought out in those years
only which are characterized by a Sunday maximum; and, accordingly, in
Chart 12 I have depicted the curves in a more suitable form.
Chart 12 _A_ is obtained by combining the data of 1888, 1892, and 1896:
the years of a Sunday maximum. Curve 12 _B_ represents the results of
1894, the year of a Tuesday maximum--multiplied throughout by three in
order to render the curve strictly comparable with the former. Curve 12
_C_ represents 1886 and 1897--the years of a Thursday maximum--similarly
multiplied by 1.5. In Curve 12 _D_ we have the results of 1887--the year
of a Friday maximum--again multiplied by three; and in Curve 12 _E_ those
of 1893 and 1895--the years of a Saturday maximum--multiplied by 1.5.
Finally, Curve 12 _F_ represents the combined results of all nine years
plus (the latter half of) 1891; and this curve shows that, on the whole
period, there is a very strongly marked Sunday maximum.
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