Proceedings of the Manchester Literary and Philosophical Society, 6th February, 1877, vol. xvi., p. 113.

Montucla. Histoire des Mathématiques, vol. iii. p. 373.

British Quarterly Review, No. lxxxvii, July 1866.

Mind, October 1876, vol. i. p. 484.

Pure Logic, Appendix, p. 82, § 192.

Elementary Lessons in Logic (Macmillan), p. 123. It is pointed out in the preface to this Second Edition, that the views here given were partially stated by Leibnitz.

Syllabus of a Proposed System of Logic, p. 29.