562. Expert evidence.

A large portion of the evidence in patent cases comprises expert evidence. The object of such evidence is mainly to instruct the court as to the state of knowledge, the meaning of terms of art or even of complete sentences or paragraphs of a technical character1 and other surrounding circumstances so as to enable the court to read the specification with the understanding of the craftsman to whom it is addressed, and to form a true opinion on the various issues raised; but it is not the function of the witness to construe the specification or other documents