— MIGRATION AND BUSINESS CYCLES
Railway maintenance is distinctly a warm-weather occupation.
being low in the first quarter of the year, then rising rapidly to a
high level in June and the following four months, then sharply
declining in November and December.
Bituminous Coal (Chart 52, Fig. C.)
For monthly employment in bituminous coal mining, we have
only the fragmentary evidence in the U. S. Census of Mines and
Quarries for 1909 and 1919 and in the data issued by the Bureau of
Labor Statistics for the two years from April, 1920, to March,
1922. An index based on these fragments appears in Curve (f) of
Chart 52, Fig. C. The second curve on this chart represents seasonal
 fluctuations in the tonnage of bituminous coal produced, in the
years 1913 to 1922, adjusted for the varying length of the months in
the year. Bituminous coal mining is characterized by a large
amount of intermittent employment, which is probably not fully
reflected in the employment statistics. For this reason, and because
 of the fragmentary nature of the direct statistics of employment,
 we have used the index of variations in production as a
measure of seasonal fluctuations in bituminous coal mining employment.

The resulting seasonal curve is almost the reverse of that computed
for railway maintenance. The period of greatest inactivity occurs
in the second quarter, notably in April, followed by an increase in
the late summer and early fall and a decline again at the close of
the year.
Anthracite Coal Mining (Chart 52, Fig. D)
The direct evidence of employment by months in anthracite coal
mining is even scantier than for bituminous coal; and, accordingly,
for an index of seasonal variation in this industry, we have utilized
a curve based upon production in the years 1913 to 1921 (see Curve
“g” Fig. D). This index exhibits only a mild fluctuation with
peaks in June and October. Employment by months in the census
years 1909 and 1919 (Curves ‘“h” and ‘‘i”’) shows an even milder
fluctuation.
Construction (Chart 53)
Seasonal fluctuations in the construction industry are of particular
 importance to the immigrant. It is a well-known fact that
a large proportion of the unskilled work in outdoor construction is

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