The great number of the useful applications of steel in the arts, which characterize the present age, have given to it the appropriate title of the Age of Steel." It has been commonly predicted that the number of uses to which this metal can be put will be largely extended, and that iron will eventually give place to steel on railways, in bridge construction, and in many other important applications. Sir William Armstrong in his recent address to the mechanical engineers at Newcastle, made some statements upon this subject that will attract the attention of the mechanical world, and will not probably pass unquestioned by those who are perhaps not less authorities on the subject than even Sir William Armstrong himself. The conclusion at which he arrives is, to use his own language, "that although steel has a much greater tensile strength than wrought iron, it is less adapted to resist con cussive strain." This conclusion is based upon the assertion that " the vibratory action attending excessive concussion, is more dangerous to steel than to iron," and also upon " the want of uniformity in steel, which still continues to be an objection to its use." It must be admitted that these views were supported with much ability. The speaker alluded to experiments made by-him some years since, on the toughening of steel in large masses by plunging it, when heated, in oil, from which he was led to expect that he would be able to produce armor plates of extraordinary resisting power. An armor plate of steel was made specially for the experiments, and was tempered in a large bath of oil. Its quality was then tested by cutting off pieces, bending and subjecting them to tension. The speaker asserted that although the result showed a very high tensile strength, combined with so much toughness that he was unable to match it by any sample of iron he could compare with it, yet when the plate was sent to Portsmouth for trial in the fullest confidence of its success, two shots from a 68 pounder sufficed to break it in various directions, and it was justly pronounced a failure. Here then we are presented with an anomaly. The best and only tests which are available to the iron master, in order to prove the strength of iron and steel, having demonstrated the great strength and tensile power of the steel in the armor plate described, it utterly failed under a trial that an iron plate of similar dimensions would undoubtedly ha"ve withstood. Now, whatever plea may be made against the vahdity of the p-eliminary test, will not avail to controvert the fact that steel is not understood, and in that fact we find, if not the proof that Sir William Armstrong is wrong in opinion in regard to the limit of the availability of steel, at least the ground for the hope that he may not be right. There are yet unpenetrated mysteries in the nature of this wonderful material, which, notwithstanding the unremitting efforts of investigators, still elude their grasp. Even the nature of the common process of tempering is, as yet, a matter of theoretical discussion, about which absolutely nothing is known positively. To entertain the belief which Sir William Armstrong avows, and in which he is partially backed by The Engineer, is to entertain the unwelcome idea, that the limit of knowledge in this field is reached. The mind of most scientists would shrink from such a conclusion ; the progress made in the manufacture of steel within the last decade forbids it; and the name and fame of the man who thus avows it, will fail to add weight enough to his views to lead to their extensive adoption.