IT is neither usual nor becoming for authors to question the judgment of a reviewer in dealing with their works, and although I think that in your number (vol. xiii. p. 441) you have treated the little work by Mr. Preece and myself with some severity, I do not propose to depart from this wholesome rule. Nevertheless, I think it but right to point out that the reason why the scientific part of the subject was so fair left out was because this had been already dealt with in another work of the same series. Prof. Fleeming Jenkin's text-book on “Electricity and Magnetism” had appeared before that on “Telegraphy” was undertaken. In the former “the part of science” had been so ably treated that it became unnecessary and would have been out of place to go over the same ground in a practical text-book which was to appear in the same series.