Experience is required in the greatest of modern inventions. Electricity, at a moderate immersion, subjected to a moderate superincumbent weight, is an effectual messenger, swift as thought; but when overweighted by immersion to depths where the superincumbent pressure amounts to thousands of pounds upon the square inch, then the messenger becomes paralysed, and refuses to obey man’s will; showing very clearly that until that pressure be artificially removed by insulating the conducting wire in tubes equal to restrain or keep from it that enormous load, the lasting success of an Atlantic telegraph is very doubtful. Many similar instances might be cited to show the necessity of considering well the established laws of nature, and their bearing on the object pursued. In no science is this of more importance than in gunnery; and the hundreds of useless inventions in gunnery are to be ascribed to the non-observance of these rules. The two-grooved rifle, the “steam gun,” “the sciva,” “Warner’s long-range myth,” and many other inventions equally absurd, engage the attention for a time, but soon vanish: in fact, all experience shows that improvement can only be effected in accordance with certain established principles of nature and practical science. Iron, in quantities sufficient for all reasonable requirements, is a dutiful servant; but, when required of colossal proportions, it refuses to obey: giving us a hint from nature, that we should be content with moderation. All the principles appertaining to science are based on certain established laws; the unsoundness of one renders the superstructure unsound also; and any deductions drawn from unsound principles are comparatively worthless. Gunnery, as a science, must be in uniformity with truth in all its parts, or no science exists in its arrangements. This will be best illustrated by dividing the subject into several heads: 1st, the explosive power and its velocity; 2nd, the retarding agents, air and friction; 3rd, the construction of the projectile tubes; and 4th, the form of projectile best calculated to attain a perfect result. 1st. The explosive power. Gunpowder has been stated by different authorities to liberate its gases with very different degrees of rapidity. Hutton has given to it a much greater rapidity than Robins has evidently even surmised; though, no doubt, as we have already shown, high velocity in gunpowder depends on several circumstances--the degree of purification of its ingredients, their intimate mechanical mixture (that the elements may exert their affinities with the utmost facility), and, lastly, the degree of granulation observed: and in addition, the suitability of the tubes or vessels for carrying on correctly such important experiments. Robins and Hutton unquestionably may be regarded as the English, if not the European, authorities, and any work on the science of gunnery would be very incomplete without their valuable elucidations.