(1)Where a patent for an invention has been applied for or granted, and the applicant or the patentee, as the case may be, applies for a further patent in respect of any improvement in or modification of the invention, he may, if he thinks fit, in his application for the further patent, request that the term limited in that patent for the duration thereof be the same as that of the original patent or so much of that term as is unexpired.
(2)Where an application containing such a request is made, a patent (herein-after referred to as a patent of addition) may be granted for such term as aforesaid.
(3)A patent of addition shall remain in force so long as the patent for the original invention remains in force, but no longer, and in respect of a patent of addition no fees shall be payable for renewal.
(4)The grant of a patent of addition shall be conclusive evidence that the invention is a proper subject for a patent of addition, and the validity of the patent shall not be questioned on the ground that the invention ought to have been the subject of an independent patent.