1. The deed of the patent right was prop erly admitted. The testimony of the plaintiff laid a foundation for proof of the acts of Stewart as his agent in selling patent rights, and the instructions of the court required the jury to give no effect to the deed unless they first found that it was duly executed by Stewart as the agent of the plaintiff. Besides; the deed, being the consideration of the note in suit, was admissible as a link in the chain of evidence.

2. The declarations of Stewart in conversation with the defendant were also admissible. They were offered as the declarations of the agent of the plaintiff while engaged in his business, and the jury were instructed to give no weight to them unless they first found the fact of the agency.

3. The witness offered as an expert had sufficient special experience and knowledge to render him competent to testify as an expert, and his testimony was properly admitted.

4. The instructions given to the jury were open to no just exception. Bliss v. Negus, 8 Mass. 46. Dickinson v Hall, 14 Pick. 217. Exceptions overruled.