Invention. As to what constitutes invention no general rule can be laid down. There are many improvements which are the natural result of the advancement of an industry and which are suggested by many persons whenever the occasion demands. There also are many changes which are merely the expected skill of an ordinary mechanic working in those lines. All such changes are not "inventions" within the meaning of the patent statutes and are not patentable.

In general, invention may be said to consist in bringing forth that which theretofore was hidden to persons skilled in that particular art. The amount of change necessary to constitute invention may be very small, or may be required to be quite radical, depending upon various factors, but principally upon the advantages and results following from the change. If the benefits are very great, and the public and manufacturers are anxious to adopt the improvement as soon as shown, it will be held to show that even a very slight change was the doing of something which before was hidden, and hence to be an invention. On the other hand, where there is no marked resulting advantage the courts require a greater degree of change in order to find the presence of invention.

Novelty. The question of the newness or novelty of an invention is purely one of fact and one upon which no opinion can be expressed without a detailed knowledge or examination of the art to which the invention relates. Under the statute, an invention is not new if it was:

1. Patented in this or any foreign country before the applicant's invention or discovery thereof, or more than two years prior to the application for patent.

2. Described in a printed publication in this or any foreign country prior to such invention or discovery, or more than two years prior to the application.

3. Known or used in this country prior to such in-invention or discovery, or

4. In public use or on sale in this country for more than two years prior to the discovery.

It follows that knowledge or use of an invention in a foreign country does not affect a patent granted in this country, unless such invention was either patented or described in some printed publication.

Novelty can be determined only by an examination of all prior patents, publications and uses in the same and analogous classes of inventions. This, to be thorough, covers a very wide range.

Term of patent. All mechanical patents are granted for the uniform term of 17 years. This is not now affected by the existence of any prior shorter term foreign patents for the same invention, the only requirement being that if a patent is first taken out in a foreign country the application in this country must be filed within 12 months after the filing of the foreign application. The term of 17 years can be extended only by a special act of Congress, and this has not been done in any case, and is not likely to be done.

In case there is a material error in the patent, or if it is inoperative or invalid by reason of a defective or insufficient specification or claim, it may be reissued, but such reissue patent will continue in force only for the unexpired term of the original patent.

Design patents are granted for terms of 3 1/2, 7 or 14 years, at the option of the applicant. He must make his selection of the term at the time he files his application. It cannot be made thereafter.

The right granted by patent. All patents give an exclusive right during the term of the patent to (1] make, (2) use and (3) sell the invention covered there by. Infringement, therefore, may occur either by making, or by using, or by selling the device. Where one party manufactures a patented device, another party sells it, and a third party uses it, they are each liable for the entire enfringement, and the patentee can choose which of the three he will use, thus being able to respond in damages.

Patent rights extend to all of the United States and territories, but not beyond the same. Vice versa, patents granted in foreign countries give no protection in this country. Therefore it it is no aid to the protection in this country to also take out patents in foreign countries. The seller or user in this country of an article manufactured abroad will be liable for infringe ment of any United States patents covering said article. A patent gives an exclusive right only for that which is distinctly claimed. If no sufficient claim is made, the courts will give no relief, even if the invention is exceedingly valuable. The utmost care should there-lore be exercised in drawing the claims of a patent. It is possible to so restrict the claims for a very valuable invention that it will be easy for others to devise forms of apparatus which accomplish the same result but do not infringe the patent. The claims should cover all possible mechanical embodiments of the principle of the invention, so that others, even though they originate new mechanical constructions or combinations, cannot avoid infringement.

Patent claims usually are drawn to combinations of the various elements which constitute the new -device. Infringement does not exist unless all elements of the claims are employed by the defendant. In other words, the combination of a claim must be used in its entirety or else infringement doesnot exist. It is therefore essential that the claim, or at least the broad claim, should contain no element of limitation which is not absolutely essential to the principle of the invention. Brevity in patent claims is desirable.

The monopoly does not begin until the patent has actually issued. While the application is still pending in the Patent Office, the inventor has no right to sue others for infringement.