This power belonging inherently to those in possession, and largely dependent for its practical utility on close unity of action, may always be worked by a trade organization to push the interests of its members independently of the supply of free outside labour, and used by slow degrees may be made a means of gaining piece by piece a considerable industrial gain.

Care must, however, be taken, never to press for a larger gain than is covered by the difficulty of replacing the body of present employes by outside labour.

Miscalculations of the amount of this inherent power of Union are the chief causes of "lock-outs" and failures in strikes.
Another weapon in the hands of unskilled combination, less calculable in its effectiveness, is the force of public opinion aided by "picketing," and the other machinery of persuasion or coercion used to prevent the effective competition of "free" labour.

In certain crises, as for example in the Dock strike of 1889, these forces may operate so powerfully as to strictly limit the supply of labour, and to shut out the competition of unemployed.

There can be no reason to doubt that if public authority had not winked at illegal coercion of outside labour, and public opinion touched by sentiment condoned the winking, the Dock strike would have failed as other movements of low-skilled labour have generally failed.