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Rh food has a tendency to become more expensive. In the enunciation of this principle, we have employed the word tendency. We believe that an example may be thus afforded, which will illustrate the great importance of enunciating almost all the principles of political economy, as exerting tendencies, rather than as producing immediate results. This has not been sufficiently recognised, and consequently the progress of political economy has been greatly retarded, and much prejudice and incredulity have been raised in the minds of practical men towards the conclusions of this science. In mathematics a force is measured by the effects which it has a tendency to produce, i.e. which it would produce if not counteracted by other forces. The force of gravity is estimated by the space through which the body would fall in a second of time, if it was acted upon by no other force; this space is sixteen feet; all bodies, however, do not so move, although every particle of matter is acted on by the same force of gravity. A feather floating in the air is attracted by the force of gravity, and yet it does not fall through sixteen feet in a second of time; the feather does not fall through this space, because its downward motion is retarded by the resistance of the air. Although the force of gravity is thus partly counteracted, it is not either destroyed or rendered nugatory; its effects may appear to be different, but the force of gravity always exerts a tendency, whether the tendency be counteracted or not, to make a body move through sixteen feet in a second of time. It would be very unreasonable to assert that the theory of mechanics was erroneous, because other forces intervene and modify the effects attributed to the action of a certain force. The distrust which is sometimes shown towards the principled of political economy is equally unreasonable; these principles attribute certain effects to certain causes, but the effects will be altered, if the causes are modified; these causes, like the forces in mechanics, are often affected in their operation by many disturbing agencies. For instance, the principle has been enunciated that the tendency of the increased demand of an advancing population is to make food more expensive. Political economy however is not in error, because