§ 5.

In consequence of the probability, or perhaps we may say the certainty, that the causes leading to the evolution of a new idea in our mind, will eventually produce a like result in some other mind, the claim above set forth must not be admitted without limitation. Many have remarked the tendency that exists for an important invention or discovery to be made by independent investigators nearly at the same time. There is nothing really mysterious in this. A certain state of knowledge, a recent advancement in science, the occurrence of some new social want,—these form the conditions under which minds of similar characters are stimulated to like trains of thought, ending as they are prone to do in the same result. Such being the fact, there arises a qualification to the right of property in ideas, which it seems difficult and even impossible to specify definitely. The laws of patent and copyright, express this qualification by confining the inventor’s or author’s privilege within a certain term of years. But in what way the length of that term may be found with correctness there is no saying. In the mean time, as already pointed out (p. 110), such a difficulty does not in the least militate against the right itself.

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