poraries, and enabled them to ascertain the time of its rotation, and the inclination of its axis. They also correctly inferred, from their appearance, the existence of a luminous envelope, in which funnelshaped depressions revealed a solid and dark nucleus. Just a century ago, Alexander Wilson indicated the presence of a second and less luminous envelope beneath the outer stratum; and his discovery was confirmed by Sir William Herschel, who was led to assume the presence of a double stratum of clouds, the upper intensely luminous, the lower gray, and forming the penumbra of the spots. Observations during eclipses have rendered probable the supposition that a third and outermost stratum of imperfect transparency encloses concentrically the other envelopes. Still more recently, the remarkable discoveries of Kirchhoff and Bunsen require us to believe that a solid or liquid photosphere is seen through an atmosphere containing iron, sodium, lithium, and other metals in a vaporous condition. Magnetism.— Guided by the same principles which have been so successful in Astronomy, its sister science, Magnetism, emerging from its infancy, has of late advanced rapidly in that stage of development which is marked by assiduous and systematic observation of the phenomena, by careful analysis and presentation of the facts which they disclose, and by the grouping of these in generalizations, which, when the basis on which they rest shall be more extended, will prepare the way for the conception of a general physical theory, in which all the phenomena shall be comprehended, whilst each shall receive its separate and satisfactory explanation. "To refer to a single instance of the elucidation of magnetic phenomena, we have seen those magnetic disturbances· so mysterious in their origin, and so extensive in simultaneous prevalence, and which less than twenty years ago were designated by a term specially denoting that their laws were wholly unknown—traced to laws of periodical recurrences; revealing, without a doubt, their origin in the central body of our system, by inequalities which have for their respective periods the solar day, the solar year, and, still more remarkably, an until lately unsuspected solar cycle, of about ten of our terrestrial years, to whose existence they bear testimony, in conjunction with the solar spots, but whose nature and causes are in all other respects still wrapped in entire obscurity. We owe to General Sabine, especially, the recognition and study of these and other solar magnetic influences, and of the magnetic influence of the moon, similarly attested by concurrent determinations in many parts of the globe, which are now held to constitute a distinct branch of this science, not inappropriately named celestial,' as distinguished from purely terrestrial magnetism. "Chemistry. The most remarkable advance in this science is that made by Bunsen and Kirchhoff, in the application of the colored rays of the prism to analytical research. We may consider their discoveries as the commencement of a new era in analytical chemistry, from the extraordinary facilities they afford in the qualitative detection of the minutest traces of elementary bodies. The value of the method has been proved by the discovery of the new metals, cæsium and rubidium, by M. Bunsen; and it has yielded another remarkable result, in demonstrating the existence of iron, and six other known metals, in the sun. "I must not, however, pass over in silence the valuable light which chemistry has recently thrown upon the composition of iron and steel. Although Despretz demonstrated many years ago that iron would com— bine with nitrogen, yet it was not until 1857 that Mr. C. Binks proved that nitrogen is an essential element of steel, and more recently, Caron and M. Fremy have further elucidated this subject; the foi. showing that cyanogen, or cyanide of ammonium, is the essential element which converts wrought iron into steel; the latter combining iron with nitrogen through the medium of ammonia, and then converting it into steel by bringing it, at the proper temperature, into contact with common coal-gas. There is little doubt that in a few years these discoveries will enable Sheffield manufacturers to replace their present uncertain, cumbrous, and expensive process by a method at once simple and inexpensive, and so completely under control as to admit of any required degree of conversion being obtained with absolute certainty. Mr. Crace Calvert also has proved that cast-iron contains nitrogen, and has shown that it is a definite compound of carbon and iron, mixed with various proportions of metallic iron, according to its nature. -- "Geology. It is little more than half a century since Geology assumed the distinctive character of a science. Taking into consideration the aspects of nature in different epochs of the history of the earth, it has been found that the study of the changes at present going on in the world around us enables us to understand the past revolutions of the globe, and the conditions and circumstances under which strata have been formed, and organic remains imbedded and preserved. The geologist has increasingly tended to believe that the changes which have taken place on the face of the globe, from the earliest times to the present, are the result of agencies still at work. But whilst it is his high office to record the distribution of life in past ages, and the evidence of physical changes in the arrangement of land and water, his results hitherto have indicated no traces of its beginning, nor have they afforded evidence of the time of its future duration. "Applied Mechanics.—During the last century the science of Applied Mechanics has made strides which astonish by their magnitude; but even these, it may reasonably be hoped, are but the promise of future and more wonderful enlargements." Referring to the progress of steam navigation, Mr. Fairbairn remarked, "that the paddle-wheel system of propulsion has maintained its superiority over every other method yet adopted for the attainment of speed, as by it the best results are obtained, with the least expenditure of power." "Great changes in the cultivation of the soil are undoubtedly destined to be effected by the steam-engine. It is but a short time since it was thought inapplicable to agricultural purposes, from its great weight and expense. But more recent experience has proved this to be a mistake; and already in most districts we find that it has been pressed into the service of the farm. The small locomotive, mounted on a frame with four wheels, travels from village to village, in Great Britain, with its attendant, the thrashing-machine, performing the operations of thrashing, winnowing, and cleaning, at less than one half the cost by the old and tedious process of hand labor. Its application to ploughing and tillage on a large scale is, in my opinion, still in its infancy; and I doubt not that many members of this Association will live to see the steam-plough in operation over the whole length and breadth of the land. Much has to be done before this important change can be successfully accomplished; but with the aid of the agriculturist in preparing the land so as to meet the requirements of steammachinery, we may reasonably look forward to a new era in the cultivation of the soil. "Iron Ship-building.—In iron ship-building, an immense field is opening before us. Our wooden walls have, to all appearance, seen their best days; and as one of the early pioneers in iron construction, as applied to ship-building, I am highly gratified to witness a change of opinion that augurs well for the security of the liberties of the country. From the commencement of iron ship-building, in 1830, to the present time, there could be only one opinion amongst those best acquainted with the subject, namely, that iron must eventually supersede timber in every form of naval construction. The large ocean steamers, the 'Himalaya,' the 'Persia,' and the Great Eastern,' abundantly show what can be done with iron; and we have only to look at the new system of casing ships with armor-plates to be convinced that we can no longer build wooden vessels of war with safety to our naval superiority and the best interests of the country. I give no opinion as to the details of the reconstruction of the navy; but I may state that I am fully persuaded that the whole of our ships of war must be rebuil of iron, and defended with iron armor calculated to resist projectile of the heaviest description at high velocities. "In the early stages of iron ship-building, I believe I was the first to show, by a long series of experiments, the superiority of wrought iron over every other description of material in security and strength, when judiciously applied in the construction of ships of every class. Other considerations, however, affect the question of vessels of war; and although numerous experiments were made, yet none of the targets were on a scale sufficient to resist more than a six-pounder shot. It was reserved for our scientific neighbors, the French, to introduce thick iron plates as a defensive armor for ships. The success which has attended the adoption of this new system of defence affords the prospect of invulnerable ships of war; and hence the desire of the government to remodel the navy on an entirely new principle of construction, in order that we may retain its superiority as the great bulwark of the nation. "It is asserted, probably with truth, that whatever thickness of plates are adopted for casing ships, guns will be constructed capable of destroying them. But their destruction will even then be a work of time; and I believe, from what I have seen in recent experiments, that, with proper armor, it will require not only the most powerful ordnance, but also a great concentration of fire, before fracture will ensue. If this be the case, a well-constructed iron ship, covered with sound plates, of the proper thickness, firmly attached to its sides, will, for a considerable time, resist the heaviest guns which can be brought to bear against it, and be practically shot-proof. But our present means are inadequate for the production of large masses of iron; and we may trust that, with new tools and machinery, and the skill, energy, and perseverence of our manufacturers, every difficulty will be overcome, and armor-plates produced which will resist the heaviest existing ordnance. "The rifling of heavy ordnance, the introduction of wrought iron, and the new principle of construction with strained hoops, have given to all countries the means of increasing enormously the destructive power of their ordnance. One of the results of this introduction of wrought iron and correct principles of manufacture is the reduction of the weight of the new guns to about two-thirds the weight of the older cast-iron ordnance. Hence follows the facility with which guns of much greater power can be worked, whilst the range and precision of fire are at the same time increased. "Iron Bridges.. We have seen a new era in the history of the construction of bridges, resulting from the use of iron; and we have only to examine those of the tubular form over the Conway and Menai Straits to be convinced of the durability, strength, and lightness of tubular constructions applied to the support of railways or common roads, in spans which, ten years ago, were considered beyond the reach of human skill. When it is considered that stone bridges do not exceed one hundred and fifty feet in span, nor cast-iron bridges two hundred and fifty feet, we can estimate the progress which has been made in crossing rivers four or five hundred feet in width, without any support at the middle of the stream. Even spans greatly in excess of this may be bridged over with safety, provided we do not exceed eighteen hundred to two thousand feet, when the structure would be destroyed by its own weight. "Importance of Good Machinery.—It is to the exactitude and accuracy of our machine-tools that our machinery of the present time owes its smoothness of motion and certainty of action. When I first entered Manchester, the whole of the machinery was executed by hand. There were neither planing, slotting, nor shaping machines; and, with the exception of very imperfect lathes, and a few drills, the preparatory operations of construction were effected entirely by the hands of the workmen. Now everything is done by machine-tools, with a degree of accuracy which the unaided hand could never accomplish. The automaton, or self-acting machine-tool, has within itself an almost creative power; in fact, so great are its powers of adaptation that there is no operation of the human hand that it does not imitate. “Telegraphy. — A brief allusion must be made to that marvellous discovery which has given to the present generation the power to turn the spark of heaven to the uses of speech;-to transmit along the slender wire, for a thousand miles, a current of electricity that renders intelligible words and thoughts. "In land telegraphy the chief difficulties have been surmounted, but in submarine telegraphy much remains to be accomplished. Failures have been repeated so often as to call for a commission on the part of the British Government to inquire into the causes, and the best means of overcoming the difficulties which present themselves. I had the honor to serve on that commission, and I believe that from the report, and mass of evidence and experimental research accumulated, the public will derive very important information. It is well known that three conditions are essential to success in the construction of ocean telegraphs, -perfect insulation, external protection, and appropriate apparatus for laying the cable safely on its ocean bed. That we are far from having succeeded in fulfilling these conditions is evident from the fact |