A patent claim for a general principle must be clearly and precisely stated in the claim itself; it cannot be inferred from the specification or results achieved. If the claim is for a specific apparatus, a device with a different mechanical operation does not infringe.

Lord Shaw of Dunfermline:-

This appeal is from a judgment of the Court of Appeal in New Zealand, dated 30th July 1914. By the judgment appealed against the Court held that the respondents had not infringed the appellants' patent. So holding, the Court found it unnecessary to decide a question raised by the defence as to utility, but an opinion was expressed that the patent was useful. The sole question which is raised on the present appeal is whether there was infringement.

It becomes accordingly necessary to see exactly what is the scope of the appellants' claim. The invention was described generally in the Armstrong specification in this way :

"This invention relates to milk releasers whereby milk is automatically delivered from the pipes of milking machines without breaking down the vacuum or stopping milking operations."

The actual claims are four in number. The respondents were not represented at the bar of the Board; and their Lordships accordingly had not the advantage of any analysis of these claims from the respondents' point of view. A question might suggest itself as to whether the construction put by the appellants' counsel upon the validity and scope of these claims is correct; but their Lordships find it unnecessary to enter upon this topic, and they confine themselves to the specific argument presented to the Board under one claim, namely, the third. That claim is as follows :

"Apparatus of the kind described wherein a vacuum formed in an upper compartment is also formed in a lower compartment upon the rising of a float, thereby obtaining equilibrium, the milk then passing from the upper to the lower compartment and escaping through an outlet valve as set forth."

The view presented was that although the claim is in terms for "apparatus of the kind described......as set forth," yet there was in gremio of it something much deeper and more far-reaching, namely, a claim for a principle. This introduces a question much debated in patent law, and their Lordships see no occasion in the present case for canvassing that question. For it appears to the Board that the claim is simply what it appears to be, namely, for the apparatus described. A certain result is, no doubt, said to be reached by this apparatus. It might be possible in very many cases of a claim for apparatus — if the argument presented were sound — to evolve a claim for a principle from a description given of the results achieved, and to maintain accordingly that it was the principle of the invention in that sense which was the real subject of the claim. This is, in their Lordships' opinion, a method of construction of patent claims which is accompanied with serious danger, and their Lordships content themselves with saying that they see no occasion in the present case for resorting to such a method.

As the present Master of the Rolls (then Cozens-Hardy, L.J.) said in Ackroyd and Best v. Thomas 21 Re. Pat. Cas. 737.

"If a patentee desires to claim a general principle it is his duty to make that intention reasonably clear. The Court ought not to be called upon to spell out such an intention from the use of ambiguous language."

To which their Lordships would add that if any claim for a principle is made it must undoubtedly appear in the claim as that claim is stated, and must not be left to an inference resting on a general review of the specification, or a general search among the language employed therein for the meritorious element of principle or idea.

The necessity for a clear and definite statement in the claim itself is in the case of an alleged principle all the greater, because whenever it is not the specific apparatus or combination which is claimed, but something underlying or stretching beyond that apparatus, the exact ambit of such a claim would require the strictest scrutiny. Otherwise it is manifest that the scope of the alleged principle might — left nebulous — embrace anything from a law of nature to the most familiar principles of statics or mechanic