  There is a further important aspect of the extent to which Perrin's experiments supported the kinetic theory. One of the major objections raised by opponents of that theory was the fact that it implied that the second law of thermodynamics is only statistically true. Perpetual motion machines of the second kind become improbable rather than impossible. It is difficult to resist the conclusion that the constant lifting of Brownian particles against gravity refutes the unqualified version of the second law. When a Brownian particle moves upwards then the first law of thermodynamics, the conservation of energy, requires that the potential energy gained by the particle must come from somewhere. If it comes from the heat of the suspending liquid then this is in contradiction to the second law. An opponent of the kinetic theory and a defender of the literal truth of the second law is required to supply some alternative source of the energy. Needless to say, no suitable alternative was forthcoming. Once the kinetic theory is assumed, the rising of a Brownian particle is understood as a the result of a statistical fluctuation. What is more, the randomness and the smallness of the scale on which the violations of the second law take place ensures that it is not possible to employ the phenomenon to extract useful work.