McArthur J., who tried the action, found that these differences in design were variations deliberately made by the appellant in the hope or expectation of avoiding infringement of the respondent's patent. He considered that, at best, the variations amounted to no more than the adoption of mechanical equivalents and that, in any case, the appellants' cup was a colourable imitation of the patented article. He accordingly held that the first claim had been infringed. I am unable to agree in this conclusion, because I think an essential feature of the claim is the use of the pin to confine the spring and to extend through the walls and project outwardly therefrom. "A claiming clause operates as a disclaimer of what is not specifically claimed, and for such disclaimer there may be reasons known to the inventor but not to the Court" (per Lord Parker, Fellows v. Thomas William Lench Ltd.[10]). It cannot be known, at any rate with certainty, why the draughtsman of the specification should restrict the monopoly he claimed by so definitely including in his description the manner in which the spring is confined between the closure member and the pin extending through and projecting outwardly from the walls. But in such a claim in respect of the nipple as a separate member of the whole combination, common knowledge, and even prior publication, may well have suggested the unwisdom of widening the claim so that it would not depend upon this feature, a feature to which originality might more plausibly be ascribed. The thing claimed is not the mechanical embodiment of a new principle. It is not a particular application of some inventive idea which may be applied to produce the same new result in other ways. It describes and claims an appliance of definite construction exhibiting specified features in combination. The claim to protection ex facie appears to be based upon the association of these features so as to produce the useful result. The question is not whether the differences of construction in the respondent's nipple and in that of the appellant are material to the utility of the appliance or to the manner of performing its function or whether ingenuity is involved in the changes. The question is: How wide is the monopoly? Once it is determined that the discarded features are essential to the claim, the substitution of other means of performing the like function cannot amount to infringement by colourable variation, or by the use of a mere mechanical equivalent. The changes are not insubstantial variations in detail under colour of which the thing claimed is taken. They are not other mechanical embodiments of the inventive idea for which protection has been obtained. The claim itself makes them cardinal. The intention of the appellant to take advantage of the narrowness of the monopoly is, of course, immaterial.