Two or more parties may contribute in developing an idea and producing an invention, which is truly the result of their joint mental efforts, and not the separate invention of either. In such case both must apply for the patent, which is granted to them jointly. But if a patent is thus issued to two and only one of them is the inventor, the patent is invalid. Nor can one of two joint inventors make application and secure the patent on assignment from the other; both must join.
The patent must issue on the application of and in the name of the real inventor even though he was employed to make it for the benefit of another. Notwithstanding, the employer is the owner of the patent and may compel the patentee to transfer it to him. Of course their respective rights may be changed by agreement. If no agreement exists, a company that employs a skilled workman to make improvements on its machinery is not entitled to the patents granted to the workman. Says Justice Duell: "An employee, performing all the duties assigned to him in his department of service, may exercise his inventive faculties in any direction he chooses with the assurance that whatever invention he may thus conceive and perfect is his individual property. The company, however, has an implied license to make, use and sell the invention."
Where a party employs another to assist him in perfecting an invention the presumption is that the employer is the real inventor of the thing produced by their joint effort. On the other hand, where a person is employed to exercise his inventive skill, because he is known to be the possessor of it, Edison for example, the presumption is in favor of the employee. Government employees may secure patents on inventions made by them during their employment, after their relationship has ceased. The government may have an implied license to use the invention without any title thereto.
Patents may be issued and reissued to assignees on the application of inventors. On the death of an inventor before a patent has been issued to him, his executor or administrator may apply therefor, who takes the patent in trust for the heirs. A foreign executor or administrator may make a similar application. He must, however, present a proper certificate of his authority to act. Likewise, a legally appointed guardian or conservator of an insane inventor may apply for and obtain a patent in trust for him.