2:2 MIGRATION AND BUSINESS CYCLES 
has been nothing in these comparisons to indicate how the volume 
of immigration or of emigration compares in number of persons 
with the corresponding change in the number of persons employe d 
To the extent that migrants are members of the working class, the 
number of arrivals less the number of departures represents a net 
addition to the number of workers seeking employment. Unless 
this net addition is accompanied by an incifease in the number of 
persons employed, the necessary result is an increase in the total 
number of unemployed persons in the United States. If, in a given 
month, the immigration of workers exceeds the emigration of 
workers by 50,000, and the increase in the number of employed in 
the United States is only 30,000, it is obvious that there has been a 
net increase of 20,000 in the number of the unemployed. 
Fully satisfactory data for making comparisons of seasonal net 
migration and changes in employment are not available, but we 
have made the best approximation we could, in the following 
manner. In the first place, for the several industries which have 
been selected, for reasons previously indicated, as particularly 
significant when studying employment opportunities for immigrants, 
we have computed an estimate of the typical number of persons 
employed in each month of the year in the pre-war period. Statis- 
tics for the year 1909 were used in determining the average number 
of workers to be assigned to each industry. This computation yields 
an estimate of the typical month-to-month change in the number 
employed in factories, bituminous and anthracite coal mining, 
railway track maintenance, and construction work, when the cyclical 
tendencies have been as far as practicable eliminated, leaving the 
joint effect of the trend and seasonal factors. Inasmuch as the 
typical net migration, by months, represents a corresponding in- 
crease or decrease in population, it is appropriate to compare 
therewith the typical change in employment which results from 
the combined influence of the growth and seasonal elements. 
The results of the employment estimates appear in Table 59 and 
Chart 55. 
For the net migration to be used in comparison with the typical 
month-to-month change in employment, we have selected the 
excess of arriving over the number of departing male aliens. This 
group includes those male aliens who are officially classified as 
temporary migrants—that is, as nonimmigrants or nonemigrants. 
Many of these come for employment purposes, and hence it ap- 
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