down that a "principle," - meaning by this use of the term a law of nature, or a general property of matter, or rule of abstract science, cannot be the subject of a patent, the doctrine, rightly understood, asserts only that a law, property, or rule cannot, in the abstract, be appropriated by any man; but if an inventor or discoverer for the first time produces an effect or result, practically, by the application of a law, he may so far appropriate that law, as to be entitled to say, that whoever applies the same law to produce the same effect or result, however the means, apparatus, forms, or arrangements of matter may be varied, practises or makes use of his invention, unless the variation of means, apparatus, method, form, or arrangement of matter introduces some new law, or creates some new characteristic, which produces or constitutes a substantially different result. For, in all such cases, the peculiarity of the invention consists in the effect produced by the application of the natural law, as an agent; and this effect is not changed by the use of different vehicles for the action of the agent, provided there is still the same agent operating substantially in the same way, to produce substantially the same effect or result.

This may be illustrated by several inventions or discoveries, for which patents have been granted, and which have been the subjects of litigation. One of the most striking of these cases is that already mentioned, of the application of a hot-air blast to the production of a particular effect in the manufacture of iron. It is very easy to say, in general terms, that no man can appropriate to himself the use of caloric, which is a substance, or element, or force in nature, bountifully supplied, as the common property of mankind. But if any man has discovered that the use of caloric in a particular manner, never before observed, will, as a universal fact, produce a particular effect of a new character upon matter, what reason can exist why he should not appropriate to himself the production of that effect by the use

of that particular agent? His appropriation, in such a case, would embrace strictly what he has invented. It may be more or less meritorious; it may have been more or less difficult or easy of discovery; it is still his invention, and any one else who does the same thing after the inventor, however he may vary the particular means or apparatus, practises that invention which the inventor was the first to discover and announce to the world. If the patent law were to say, in this case, that the invention or discovery could not be appropriated by him who had made it, because caloric is the common property of all men, it would be obliged, in consistency, to say that a certain arrangement of wood and iron, constituting a new machine, could not be appropriated by the inventor, because cohesion, gravitation, and the laws of motion, which are all applied by the inventor to the accomplishing a certain effect, are the common property of every man. But the patent law does not come to such determinations. It proceeds upon the truth, that while the properties of matter, the forces or elements of nature are common property, any man who applies them to the production of a new and useful effect in matter may rightfully claim to have been the inventor of that application to the purpose of that effect. The ef fect itself is what is commonly regarded as the patentable subject; but as that particular effect must always be produced by the application of the same properties of matter, or the same forces or elements in nature, it is correct to say that the appropriation rightfully includes their application to the production of the effect, and that to this extent they may be appropriated.

Inventions which consist in the application of the known qualities of substances, extend the appropriation of the inventor to those qualities in the same manner and in the same sense. For instance, in the case of Walton's improvement in the manufacture of cards for carding wool, &c., which consisted in giving elasticity and flexibility to the

backs of the cards, by making the sheet on the back, in which the teeth are inserted, of India-rubber, instead of leather. The qualities of elasticity and flexibility in Indiarubber were common property; but this did not prevent the inventor from sustaining a patent, which was held to cover the general ground of giving to the backs of cards elasticity and flexibility derived from India-rubber, by whatever form of application of the India-rubber the effect might be produced.*

In the same manner, inventions which consist in the application of a well-known law of physical science, involve and admit of the appropriation of that law in its application to the production of the particular effect, however the machinery or apparatus may be varied. There is a known law of physics, that the evaporation of a liquid is promoted by a current of air, and this law is common property. An invention of certain improvements in evaporating sugar consisted in applying this law by forcing atmospheric air through the liquid syrup by means of pipes, the ends of which were carried down nearly to the bottom of the vessel containing the solution; and it is obvious that any person who should apply the same law to the same purpose, though by a different apparatus, would practise the same invention. Although, therefore, it is not safe, in reasoning upon the patent law, to lay down general rules of an abstract character, with the purpose of describing what every inventor appropriates to himself, without regard to the particular circumstances of the invention, yet it is, on the other hand, equally unsafe to assume, because the properties of matter, or the laws of physics, or the forces of nature are common property, that no inventor can establish a claim of a general character, irrespective of particular methods or forms of matter, to the application of such properties, laws, or forces in the production of a certain effect.

*See Post, § 312, § 322-327.

It is, in truth, wholly incorrect to say that the inventor in such cases, because his patent is held to embrace such a general claim, monopolizes the law, property, or quality of matter which he has applied by a particular means to the accomplishment of a certain end. His patent leaves the law, property, or quality of matter precisely where it. found it, as common property, to be used by any one, in the production of a new end by a new adaptation of a different character. It appropriates the law, property, or quality of matter only so far as it is involved in the subject with which, the means by which, and the end for which the inventor has applied it; and this application constitutes the essence and substance of the invention in all cases, and is in reality what the patentee has invented. He cannot be deprived of it without violating the principles on which all property in invention rests, and denying the whole policy of the patent law. The test which marks the extent and nature of his just appropriation is the same. that is applicable to every invention.

This test may be stated thus: That the truth, law, property, or quality of matter, which, by reason of its application, enters into the essence of an invention, may be appropriated, to the extent of every application which, according to the principles of law and the rules of logic, is to be deemed piracy of the original invention.

One of the most well-settled as well as soundest doctrines of the patent law is, that where form, arrangement of matter, proportion, method of construction, or apparatus employed are not of the essence of the invention, any changes introduced in them which do not effect a change in the characteristic or purpose of the invention, are changes in immaterial circumstances. When the patent is a patent for form, or particular arrangement, or for the apparatus devised to accomplish a particular effect, changes in these respects will be changes in the subject-matter of the invention; but in cases where the invention has a

characteristic or an aggregate of characteristics, independ ent of particular form, method, arrangement, or apparatus, changes in these things amount only to the substitution of one equivalent for another, unless they cause a change in the characteristic, essence, or, as it is commonly called, the principle of the invention. This is very clearly seen in the case of machinery. The characteristic or principle of the invention consists in producing a certain effect by the application of motion, through a form of apparatus adapted to that result. But if the same effect of the combined operation of the different parts of the mechanism can be produced by substituting a different contrivance, which does not change the characteristic of the machine, but is a mere equivalent for the part for which it is substituted, such a substitution is only a different mode of practising the same invention.

In this sense, all inventions are independent of form, except those whose entire essence, purpose, and characteristics begin and end in form alone; as would be the case with the manufacture of a sphere or a cube for the first time; and as is the case with all manufactures, the utility and advantage and proposed object of which depend on form. But where there is a purpose that does not begin and end in form alone, where the form or arrangement of matter is but the means to accomplish a result of a character which remains the same through a certain range of variations of those means, the invention is independent of form and arrangement to this extent, that it embraces every application of means which accomplishes the result without changing its nature and character. In other words, it may be stated as a general proposition, that in the characteristic or principle of an invention are embraced the truth, law, property, or quality of matter which is applied to the production of a result, and the result of such application; and that, by reason of such application, the