The complete specification for letters patent No. 133 in the amended form in which it was ultimately accepted purported to relate to "writing instruments of the type in which a ball is mounted for rotation in a housing with part of the ball exposed and is supplied with ink from a suitable reservoir, the arrangement being such that as the ball is rotated such as by being moved relatively to and in contact with a writing surface the ball carries a quantity of ink through the housing, which ink is deposited on said surface and a trace is made." An object of the invention was said to be to improve the construction of instruments of that type. According to the applicant he provided "an instrument of the type specified, having the ink reservoir constituted by a vented tube of capillary size in which when charged with viscous ink a continuous liquid vein is maintained extending from the ball, and having a feed duct leading from the reservoir to the ball, the cross-sectional area of which duct, particularly that portion adjacent the ball, being less than that of the reservoir". The italics again are mine and draw attention to two expressions concerning which there was considerable discussion. The expression "vented tube of capillary size" is employed in the specification "in relation to the reservoir of a writing instrument of the type specified to mean a tube having an internal bore of between 1 and 4 mm. (subject to a manufacturing tolerance of the order of +, -, 5%) so that when charged with a viscous ink the meniscus formed at the end of the ink column remote from the ball (at the interface between the ink, the air and the interior surface of the tube) is stable and will not break under shocks to which the instrument is subjected in normal use." Claim 1, which it is alleged the respondent's instrument infringes, is in the following terms: - "An instrument of the type specified, having the ink reservoir constituted by a vented tube of capillary size in which when charged with viscous ink a continuous liquid vein is maintained extending from the ball, and having a feed duct leading from the reservoir to the ball, the cross-sectional area of which duct, particularly that portion adjacent the ball, being less than that of the reservoir." The references which I have made to the specification are brief but they are sufficient, at least, to enable the two points made by the respondent concerning vagueness and ambiguity to be appreciated. In the first place it was said that the words of the claim "the cross-sectional area of which duct, particularly that portion adjacent the ball, being less than that of the reservoir" make it quite impossible to determine whether the claim was intended to cover any instrument in which the cross-sectional area of the feed duct or any part thereof is the same as or greater than that of the reservoir. Concerning this submission Sholl J. said: - "It was next said that the expression, "the cross-sectional area of which duct, particularly that portion adjacent the ball, being less than that of the reservoir", was ambiguous, in that it was impossible to be certain whether an instrument having the feed duct so constructed that the portion of it adjoining the reservoir was of the same cross-section as the reservoir, or of larger cross-section, while the portion of it adjacent to the ball was of smaller cross-section than the reservoir, did or did not infringe the claim. It was said by Mr. Shelley on the other hand that the word "particularly" merely provided emphasis, and that if any portion of the feed duct were of the same cross-section as or greater cross-section than the reservoir, there would be no infringement, except possibly in the case of a mere "colorable departure" within the doctrine of Clark v. Adie [1] . In the end, I have come to the conclusion that there is here an invalidating ambiguity. I am rather disposed to think the draftsman of claim 1 wanted to have the best of both worlds, and that he may have thought he was saying, in effect, - "I claim a monopoly in all instruments in which, in addition to the other three characteristics earlier mentioned, there is a feed duct leading from the reservoir to the ball, and having a lesser cross-section than the reservoir; but I go further than that, and I also claim all those with the same three previously mentioned characteristics, and a feed duct leading from the reservoir to the ball, if the portion of the feed duct adjacent to the ball has a lesser cross-section than the reservoir, whatever be the cross-section of the rest of the duct". Now that is just the opposite of the construction which Mr. Shelley sought to give the claim, although, as a matter of literal interpretation, there is much to be said for his reading of it. I simply do not know with any reasonable certainty which meaning the draftsman really intended, and there is no evidence on which I can say that the ordinary person skilled in the art of making pens, to whom the specification is addressed, could be reasonably certain. The matter is perhaps made more rather than less difficult by the fact that, as Mr. Shelley stated early in the hearing, and as the technical evidence made clear, the element of the feed duct and its cross-sectional area is not technically essential at all to the operation of the capillary tube as a non-leaking reservoir, but is merely a convenient feature for the purpose of feeding an appropriately small amount of ink to the ball point of a practical pen. The patentee has chosen, for reasons associated (as will later appear) with the objections of the examiner, to claim a combination including this fifth element, but it cannot be said with certainty what the element is, and accordingly I think the first claim, and therefore all the claims, are invalid for ambiguity and uncertainty." I confess that I do not experience the same degree of difficulty which his Honour experienced. It is true, of course, that the language of the claim is by no means clear but this does not conclude the matter. Imperfections of expression constantly give rise to difficulties in construction but only occasionally is a court driven to the necessity of saying that no reasonable meaning can be found for the words used. In the present case it is clear that the reservoir, consisting of a vented capillary tube as described is not to exceed 4 mm. + 5% for manufacturing tolerance. From one end of this reservoir - if indeed no part of the feed duct itself should properly be regarded as part of the reservoir - a feed duct provides access for ink to the internal side of the rotatable ball. Now claim 1 stipulates that the cross-sectional area of the feed duct shall be less than that of the reservoir and if the language of the claim stopped there the present contention could not have been advanced. The difficulty, if there be one, arises from the interpolation of the words "particularly that portion adjacent the ball". The interpolation of these words does not make for clarity and literally does not make sense. But while it is clear that "the function of the claims is to define clearly and with precision the monopoly claimed, so that others may know the exact boundaries of the area within which they will be trespassers" (per Lord Russell of Killowen in Electrical & Musical Industries Ltd. v. Lissen Ltd. [1] ), it is equally clear that it is the duty of the court to endeavour to ascertain from the language used the true meaning of any claim or claims. It is not the function of the court lightly to discard the claims in a specification on the ground that the language used is vague and uncertain. Now, in the present case do the words used, bearing in mind the interpolation, bear any reasonable meaning? I think they do. It is clear that the cross-sectional area of the reservoir may vary from 1 mm. to 4 mm. so that in concerning oneself with the feed duct - if it be entirely separate and distinct from the reservoir - it is necessary to visualize a duct leading from a vented tube which may have a cross-sectional area of 1 mm. or 4 mm. or somewhere between those specifications. It would be quite foreign to the conception of a feed duct that the cross-sectional area of any part of it should exceed that of the reservoir from which it leads and the terms of claim 1 read without the interpolated words make it clear that no such thing was intended. Nor, in my opinion, is the effect of the interpolated words to indicate otherwise. Their purpose, it seems to me, is to indicate that particular attention must be devoted to that portion of the feed duct adjacent to the ball. The degree to which the cross-sectional area of the feed duct must be diminished below that of the reservoir will depend primarily upon the cross-sectional area of the latter. The ball is described as having a diameter "in the order of 1 mm." so that it is apparent that where the cross-sectional area of the reservoir is of the maximum specified the degree to which the cross-sectional area of the feed duct must ultimately be diminished may be relatively great. In other cases it may be very little. In my view the purpose of the expression "particularly that portion adjacent the ball" must be taken to have been used with this circumstance in mind, and it was intended to indicate that, notwithstanding some general narrowing of the feed duct at or after its junction with the reservoir, a particular diminution was required at the point adjacent to the ball. This being so, I am of the opinion that the respondent's first submission on this aspect of the case should be rejected.