126 ECONOMIC PRINCIPLES

It serves to attract additional supplies of labour to the place
or industry in which it is realised, and may thus gradually
remove the cause of the excess, namely, the relative scarcity
of labour. Should artificial barriers restrict such recruiting
of labour supplies under the attraction of favourable conditions
 of employment, the excess may endure for a long time.
The invention or extension of other means of production, so
as to avoid dependence on the scarce labour, or the substitution
 of a cheaper (or different) product for that dependent
on such labour, may lead to a fall in the demand-price for it,
even if the supply is effectually restricted.
In a manner corresponding to that which affords peculiarly
advantageous conditions to labour which is scarce, conditions
exceptionally unfavourable may affect bodies of labourers
who are unable, or unwilling, to transfer themselves to other
localities or trades when their own occupation ceases to be
profitable. A price for their labour which would not have
sufficed to bring them into the trade or locality may yet fail
to reduce the supply to an amount which can be profitably
employed at such adequate wages. The over-supply will
lead to one of two results. Part of the labourers may be
without employment, and thus constrained by exceptional
pressure to remove themselves from the over-crowded trade
or locality. Or, the whole may find employment at wages
reduced to the level of the marginal productivity of the
excessive supply. In the event of the lack of profitable
employment being expected to be but temporary, reduced
wages, or temporary lack of work, may do nothing to reduce
the labour supply. Employers may even retain workmen at
wages higher than their temporary productiveness would
warrant, in order to hold together the working force in
anticipation of revived activity in business. Otherwise, time
may be expected to gradually reduce the over-supply, since
the irregular employment, or low wages, or both, prove an
insufficient attraction to draw young men into the trade in
numbers sufficient to replace the natural loss by death or
disability. The deficiency in the wages, during the period
of over-supply, below the level which would serve to maintain
a due flow of fresh labour into the trade, to replace its