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 184 Pateiits. [Ch.X. Sec.II. carry a reasonable knowledge of the subject-matter with him, in order clearly to comprehend specifications of this, nature, though fairly intended to be made (a). In the first place the specification is insufficient if it be ambiguous, or give directions which tend to mislead the pub- lic {b). If articles are put into a specification merely to puz- zle, or are not useful for the purpose of the patent, it is void (c). So where the patent was for making a particular sort of yellow, and the patentee directed any sort of fossil salt to be used; when only one sort of it would answer the purpose ; the patent was held void (d). An ambiguity may arise from the specification stating as essential parts, any thing which forms a part of a prior invention ; for the public are not to be deceived by the patentee holding out as material, those things which in] fact are not so {e). The patentee must, in his claims to novelty, confine himself sdlely to that which is his invention {J"). The patent must not be more extensive than the invention : and where the patent is for an improve- ment or addition, the patent and specification (g) must not be for the whole machine or manufacture, and the latter must describe precisely in what the alleged improvement consists ; so that what is old, may be distinguishable from what is new [k). As observed by Lord Ellenborough {i), <* the pa- tentee in his specification ought to inform the person who consults it, what is new, and what is old. He should say, my improvement consists in this, describing it by words if he can, or, if not, by reference to figures. But here the improve- ment is neither described in w^ords nor by figures, and it would not be in the wit of man, unless he were previously acquainted - with the construction of the instrument, to say what was new and what was old. The specification states, that the improved instrument is made in manner following : this is not true, since the description comprises that which is old? as well as that (a) 11 East, 113. (/) 11 East, 109. See per Sir Vic. (&) 1 T. R. 602. Gibbs, in Bovill v. Moore, cited Davie?, (c) Rex V. Ackwright, Bui. N. P. 398. •77. Davies, 118. / (g) See Rex o. Ackwright, 1TS4, cor. (rf) 1 T. R. 602. BuUer, Bui. Nis. Pri. 76, c. Bridgm. {e) See Lord Ellenborough's Obser- ed. 1 1 East, 1 09. vationsiii Huddart v. Grimshaw, Da- (h) 1 Stark. 199. Davies, 411. vies, 279, 294, 5. (i) 1 Stark. 201. which