delivered the opinion of the Court
This is. the same' case which was formerly before *424this Court, and is reported in 3 Wheat. Rep. 454. and by a reference to that report, the form of the patent, the nature of the action, and the subsequent proceedings, will fully appear. The cause, now comes before us upon a writ of error to the judgment of the Circuit Court, rendered upon the new trial, had in pursuance of the mandate of this Court.
Upon the new trial several exceptions were taken by the counsel for the plaintiff. The first was to the admission of a Mr. Frederick, as a witness for the defendant. It is to be observed, that the sole con» 7 trov3.rsy between the parties at the new trial was, whether the plaintiff was entitled to recover for an breach of his patent by the defendant in using the improved Hopperboy. Frederick, in his examination on the voir dire, denied that he had any interest in the cause, or that he was bound to contribute to the expenses of it. He said he. had not a Hopperboy in his mill at present, it being then in Court; that it was in his mill about three weeks ago, when he gave it to a person to bring down to Philadelphia; and that his Hopperboy spreads and turns the meal, cools it some, dries it, .and gathers it to the bolting chest. Upon this evidence the plaintiff’s counsel contended that Frederick was not a competent witness, but the objection was overruled by the Court.. It does not appear from this examination whether the Hopperboy used by Frederick was that improved by the plaintiff, or not; but assuming it was, we are of opinion that the witness was *425rightly admitted. It is perfectly clear, that a person having an interest only in the question, and not in the event of the suit, is a competent witness ; and in general the liability of a witness to a like action, or his standing in the same predicament with the party sued, if the verdict cannot be given in evidence for or against him, is an interest in the question, and does not exclude him. If nothing had been in controversy in this case, as to the validity of the patent itselt, and the general issue only had been pleaded, the present objection would have fallen within the general rule. But the:special notice in this case asserts matter, which if true, and found specially by the jury, might authorize the Court to adjudge the patent void, and it is supposed that this constitutes such an interest in Frederick in the event of the causé, that he is thereby rendered incompetent. But in this respect, Frederick stands in the same situation as every other person in the community. If the patent is declared void, the invention may be used by the whole community, and all persons may be said to have an interest in making it public property. But this results from a general principle of law, that a party can take nothing by a void patent; and so far as such an interest goes, we think it is to the credit and not to the competency of the witness. It is cleairthat the verdict in this case, if given for Evans, would not be evidence in a suit against Frederick, but Frederick would be entitled to contest every step in the cause, in the same manner as if no such suit had existed. Non constat, that Frederick himself will ever be sued by the plaintiff, or that if *426sued, any recovery can be had against him, even if the plaintiff’s patent should not be avoided in this suit. It therefore rests in remote contingencies, whether Frederick will, under any circumstances, have an interest in the event of this suit, and the law adjudges the party incompetent only when he has a certain, and not a contingent interest. It has been the inclination of Courts of law in modern times, generally, to lean against exceptions to testimony. This is a case which may be considered somewhat anomalous ; and we think it safest to admit ^ testimony, leaving its credibility to thejury.
Another exception was to the refusal of the Court to allow a deposition to be read by the plaintiff, which had been taken according to a prevalent practice of the State Courts. It is not pretended that the deposition was admissible according to the ° positive rules of law, oiMhtf rules of the Circuit Court'; and it is hot now produced, so that we can see what were the circumstances under which it was taken. No ¡practice, however convenient, can give validity to depositions which are not taken according to law, or the rules of the Circuit Court, unless the parties expressly waive the objection or, by previous consent, agree to have them taken and made evidence. This objection, therefore, may at once Jjg dismissed,
The principal arguments, however, at the bar have been urged against the charge given by the Circuit ■ Court tn summing up the cause to the jury. The charge, is spread in extenso upon the record, a practice which is unnecessary and inconvenient, and may give rise to minute criticisms and observations *427apon points incidentally introduced, for purposes of argument or illustration, and by no means essential to the merits of the cause. In causes of this nature we think "the substance only of the charge is to be examined; and if it appears, upon the whole, that the law was justly expounded to the jury, general expressions, which may need and would receive qualification, if they were the direct point in judgment, are to be understood in such restricted sense,
It has been already stated, that the whole controversy at the trial turned upon the use of the plaintiff’s Hopperboy ; and no other of the inventions, included in his patent, was asserted or supposed to be pirated by the defendant.
The plaintiff, with a view to the maintenance of his suit, contended, that his patent, so far as respected the Hopperboy,. had a double aspect. 1. That it was to be as a patent for the whole of the improved Hopperboy, that is, of the whole machine as his own invention. 2. That if not susceptible of this construction, it was for an improvement upon the Hopperboy, and he was entitled to recover against the defendant for using his improvement. The defendant admitted that he used the improved Hopperboy, and put his defence upon two grounds: 1. That if the patent was for the whole machine, i. e. the improved Hopperboy, the plaintiff was not the inventor of the improved Hopperboy so patented: 2. That if the patent was for an improvement only upon the Hopperboy, the . specification did not describe. the nature and extent of the improvement: *428and if it did, still the patent comprehended the whole machine, and was broader than the invention. To the examination of these points, and summing up the evidence, the attention of the Circuit Court was exclusively directed ; and the question is, whether the charge, in respect to the matters of law involved in these points, was erroneous to the injury of the plaintiff.
We will consider the points- in the same order in which they were reviewed by the Circuit Court. Was the patent of the plaintiff, so far as respects his improved Hopperboy, a patent for the whole machine as his. own invention ? It is not disputed that the specification does contain a good and sufficient description of the improved Hopperboy, and of the manner of constructing it; and if there had been any dispute on this subject, it would have been matter of fact for the jury, and not of law for the decision of the Court. The plaintiff, in his specification, after describing his Hopperboy, its structure, and use, sums up his invention as follows : “ I claim as my invention, the peculiar properties or principles which this machine possesses, in the spreading, turning, and gathering the meal at one operation, and the rising and lowering of its arms by its motion, to accommodate itself to any quantity of meal it has to operate upon.” From this manner of stating his invention, without any other qualification, it is apparent that it is just such a claim as wmuld be made use of by the plaintiff, if the whole machine was substantially in its structure and combinations new. The plaintiff does not state *429it to be a specific improvement upon an existing machine, confining his claim to that improvement, but as an invention substantially original. In short, he claims the machine as substantially new in its properties and principles, that is to say, in the modus operandi. If this be true, and this has been the construction strongly and earnestly pressed upon this Court by the plaintiff’s counsel, in the argument at the present term, what are the legal principles that flow from this doctrine ? The Patent Act of the 21 st of February, 1793, ch. 1!. upon which the validity of our patents generally depends, authorizes a patentto the inventor, for his invention or improvement iu any new and useful art, machine, manufacture, or composition of matter not known or used before the application, It also gives to any inventor of an improvement in the principle of any machine, or . in the process of any composition of matter which has been patented, an exclusive right to a patent for his improvement ; but he iá not to be at liberty to use the original discovery, nor is the first inventor at liberty to use the improvement. It also declares that simply changing the form or the proportion of any machine or composition of matter, in any degree, shall not be deemed a discovery. It farther provides, that on any trial for a violation of the patent, the party may give in evidence, having given due notice thereof, any special matter tending, to prove that the plaintiff’s specification does not contain the whole truth relative to his discovery, or .contains more than is necessary to produce the effect, (where the addition or concealment shall appear to have been to *430deceive .the public,) or that the thing secured by the patent was not originally discovered by the patentee, but had been in use, or had been described m some public work anterior to the.supposed discovery of the patentee, or that he had surreptitiously obtained a person’s invention ; and provides that in either of these cases judgment shall be rendered for the plaintiff, with costs, ?nd the patent shall be declared void. It farther requires, that every inventor, before he can receive a patent, shall swear or affirm to the truth of his invention, “ and shall deliver a written description of his invention, and of the manner of using, or process of compounding the same, in such futí, clear, and exact terms, as to distinguish the same from all things before kqownj and to enable any person skilled in the art or science, of which it -is a biáncb, or with which it is most nearly connected, to make, compound, and use the same; and in the case of any machine, he shall fully explain the several modes in which heffiap contemplated the application . of the principle, or character by which it may be distinguished frpm other inventions.”
From this enumeration of the provisions of the act, it is clear that the party cannot entitle himself to a.patent for more than his own invention ; and if his patent includes things before known, or before in use, as his invention, he is not entitled to recover, for his patent is broader than his invention. If, therefore, the patent be for the whole of a machine, the party can maintain a title to it only by establishing that it is substantially new in its structure and mode of operation. If the same combinations existed be*431fore in machines of the same nature, up to a certain point, and the party’s invention consists in adding some new machinery, or some improved mode of operation, to the old, the patent should be limited tosuch improvement, for if it includes the whole machinery, it includes more than his invention, and the refore cannot be supported. This is the view of the law on this point, which was taken by the.Circuit Court. That Court went into a full examination of the testimony, and also of the structure of Evans’ Hopper-boy, and Stouffer’s Hopperboy, and left it to the jury to decide, whether, up to a certain point, the two machines were or were not the same in principle. If they were the same in principle, and merely differed in form and proportion, then it was declared that the plaintiff was not entitled to recover; or, to use the language’ of the Court, if the jury were of opinion that the plaintiff was not the inventor of the Hopperboy, he was not entitled to recover, unless ■ his was a case excepted from the general operation of the act. We perceive no reason to be. dissatisfied with this part of the charge ; it left the fact open for the jury, and instructed them correctly as to the law. Ano the verdict of the jury negatived the right of the plaintiff, as the inventor of the whole machine. The next inquiry before the Circuit Court was, whether the plaintiff’s case was excepted from the general operation of the act. Upon that it is unnecessary to say more than that the. point was expressly decided by this Court in the negative, upon the former writ of error. And we think the opinion of this Court, delivered on that occasion, is correctly under*432stood and expounded by the Circuit Court. It could never have been intended by this Cour{ to declare, jn ,jjrect opposition to the very terms of the patent act, that a party was entitled to recover, although he should be proved not to have been the inventor of the machine patented ; or that he should be entitled to recover, notwithstanding the machine patented was in use prior to his alleged discovery. There is undoubtedly a slight error in drawing up the judgment of the Court upon the former writ of error; but it is immediately corrected by an attentive perusal of the opinion itself. And we do not think that it can.be better stated.or explained than in the manner in which, the Circuit Court has expounded it.
We are then. led to the examination of the other point of view in which the plaintiff’s counsel have attempted to maintain this patent. ' That is, by considering it, not as a patent for the whole of the machine or improved Hopperboy, but as an improvement of the Hopperboy. Considered under this aspect, the point presents itself which was urged by the defendant’s counsel, viz. that if it be a patent for ah improvement, it is void, because the nature and extent of the improvement is not stated in the specification. The Circuit Court-went into an elaborate examination of the law applicable to this point,, and into á construction of the tferms of the patent itself, and came to the conclusion that no distinct improve- . merit was specified in the patent; that such specification was necessary in a patent.for an improvement, and that for this defect, the plaintiff was not entitled to recover, supposing his patent to be for an improve*433ment only of an existing machine. It may be justly doubted, whether this point at all arises in the cause; for the very terms of the patent, as they have been already , considered, and as they have been construed at the bar-by the plaintiff’s counsel, at the. present ■argument, seem almost conclusively to establish, that the patent is for the whole machine, that is, for the whole of the improved Hopperboy, and not for a mere improvement upon the old Hopperboy. But, waiving this point, can the doctrine asserted at the bar be maintained, that no specification of an improvement is necessary in the patent; and that it is sufficient if it be made: out and shown at the trial, or may be established by comparing the machine specified in the patent with former machines in use? That there is po specification of. any distinct improvement in the present patent, is not denied; that the patent is good without it, is the subject of inquiry. Let this be decided by reference to the patent act.
The third section of. the patent act requires, as has been already stated, that the party u shall deliver a written description of his invention, in such full, clear, and exact terms, as to distinguish the same from all other things before known, and to enable any person skilled in the art or science, &c. Src, to make, compound, and use the same.” The specification, then, has two objects; one is to make known the manner of constructing the machine (if the invention is of amachine) so as to enable artisans to make and use it, and thus to give the public the full benefit of the discovery after the expiration *434of the patent. It is not pretended that the plaiutiiFs patent is not in this respect sufficiently exact and minute in the description. But whether it be so or not, is not material to the present inquiry. The other ubject of the specification is, to put the public in possession of what the party claims as his own invention, so as to ascertain if he claim any thing that is in common use, or is already known, and to guard against prejudice or injury from the use of an invention which the party may otherwise innocently suppose not to be patented. It is, therefore, for the purpose of warning an innocent purchaser or other person using a machine, of his. infringement of the patent ; and at the same time of taking from the inventor the means of practising upon the credulity or the fears of other persons, by pretending that his invention is more than what it really is, or different from its ostensible objects, that the patentee is required to distinguish his invention in his specification. Nothing can be more direct than the very words of the act. The specification must describe the invention “ in such full, clear, and distinct terms, as to distinguish the same from all other things before known.” How-can that be a sufficient specification of an improvement in a machine, which does not distinguish what the improvement is, nor state in what it consists, nor how far the invention extends ? Which describes the machine fully and accurately, as a whole, mixing up the new and old, but does not in the slightest degree explain what is the nature or limit of the improvement which the party claims as his own ? It seems to us perfectly clear that such a specification *435is indispensable. We do not say that the party is bound to describe the old machine; but we are of opinion that he ought to describe what his own improvement is, and to limit his patent to such improvement. For another purpose, indeed, with the view of enabling artizans to construct the machine, it may become necessary-for him to state so much of the old machine as will make his specification of the structure intelligible. But the law is sufficiently complied with in relation to the other point, by distinguishing, in full, clear, and exact terms, the nature and extent, of his improvement only.
We do not consider that the opinion of the Circuit Court differs, in any material respect, from this exposition of the patent act on this point; and if the plaintiff’s patent is to be considered as a patent for an improvement- upon an existing Hopperboy, it is defective in not specifying that improvement, and therefore the plaintiff ought not to recover.
Upon the whole, it is the opinion of the majority of the Court, that the judgment of the Circuit Court ought to be affirmed with costs.
«3 Wheat. Rep. £19,
3 Wheat.Rep. 513.