Moreover, it is seldom if ever the case that a useful invention, meeting a popular want, and therefore having a large commercial value, is in any sense the product of one man. As a general rule, the patentee who enjoys the right to the invention has actually added to the old stock only a single detail. It may be that this detail was the one thing required to make the invention practically useful; but it is certain that the addition could never have been made if the previous knowledge had not existed, and it is at least an open question whether the community ought to grant to the last man an exclusive right to the whole inheritance. Volta discovered--invented, if you please--the mode of generating a current of low-tension electricity, which has been ever since, with certain modifications, in general use; Oersted and Ampere discovered the magnetic effects of this electrical current; Faraday, again, learned how to produce an electric current from a magnet, and invented the original dynamo-machine; Henry discovered the conditions under which the magnetic effects of an electric current might be produced at great distances from the source of the power. All these men were inventors of the highest order, whose inventions have never been excelled either in the ingenuity displayed, or in the influence exerted on the welfare of mankind. Moreover, these far-reaching inventions were a willing contribution to the world's knowledge, for which no pecuniary compensation was either asked or received. Is it not, then, a question if any man of the present day has a right to the exclusive use of these inventions; for writing messages at a distance, for transmitting sound over wires, or for any purpose whatsoever? There is of course another side to the question, and I freely admit the difficulty of the problem which our patent laws present; but I feel that in their present condition they do more harm than good, and do injustice more frequently than they protect right. I greatly doubt if it is safe to grant by statute property in any invention or discovery beyond the definite mechanical contrivance in which it is for the time embodied. To grant the sole use of a well-known power of Nature to produce a specific effect, although the effect be a novel one; to give the monopoly of a process of Nature to the man who was the first to claim it; above all, to grant the sole right to make a specified mixture of materials--is certainly a policy which directly encourages vast monopolies, that tax the public without rendering a corresponding benefit.