no impression upon the iron sides, what is ent be considered little recommendation to a the use of hammering at the long range? The hammering will tell with repetition, or if it does not, the conclusion must be that ships in armor cannot hurt each other, and that their arms are no more formidable to each other than ladies' fans. But every screw iron ship has the vulnerable place of Achilles in the heel, to that point fire will be directed, as a single shot hitting the screw would disable the vessel, make her a mere log on the water at the mercy of her enemy. From All the Year Round. DR. WILKINS' PROPHETIC DREAMS. INSTANTANEOUS and, in case of need, secret communication has advanced within a few years through the successive phases of a wild vision, a bare possibility looming in the distance, a reality too strange to be fully appreciated, and an ordinary matter of fact. That it was a short time ago the first, is as certainly true as that it is regarded now as a mere sixpenny convenience, but, like many other of the most important and interesting discoveries of modern science, before even the knowledge of which it is born had come into the world, telegraphy had its prophetic announcement. Shortly after the discovery of printing, and the religious and political ferment that followed closely upon that discovery, there was an amount of speculative prescience among the pursuers of science that has at no other time been equalled. Men were not overloaded with facts, and they allowed their imaginative and poetic faculties full play. Very vague and uncertain, no doubt, was the glimpse of futurity they got; but it was often real, and much of it has since been fully verified. It is now just two centuries ago that the Honorable Society of Gray's Inn selected as their preacher the Reverend Dr. John Wilkins, at that time a puritanical clergyman, in the forty-sixth year of his age, not unknown to his contemporaries, but chiefly remarkable for his great skill in what were then called "the mathematicks." Preachers were then, as now, selected for the Inns of Court with the liberal toleration that looks straight at a man's worth, and Dr. Wilkins was an able, earnest clergyman, as well as the author of works on the physical science of his day, which might even at pres society of gentlemen learned in the law. He was one of that small but distinguished body of learned men to whom England is indebted for the foundation of the "Royal Society for the Improvement of natural Knowledge "-a body which has since included, and still includes, most of those who have chiefly distinguished themselves in the pursuit of science in England. Appointed warden of Wadham College, Oxford, in 1648, during the troublesome political disturbances of the great rebellion, Dr. Wilkins does not seem to have meddled much with politics, but, marrying a sister of Oliver Cromwell, then Protector of England, he naturally attached himself to the ruling party. His time, however, at Oxford was occupied in pursuits congenial to his tastes, for there were held at his rooms those meetings, commenced at the lodging of Dr. Petty, at which were assembled the Honorable Mr. Robert Boyle, Dr. Willis, Mr. Ashmole (founder of the Ashmolean museum), Dr. Seth Ward (afterwards Bishop of Salisbury), Dr. (afterwards Sir Christopher) Wren, Dr. (afterwards Sir William) Petty, and many others. These kindred spirits discussed subjects antiquarian, astrologic, medical, and mechanical, rather than political, and laid the foundation of a club which afterwards ripened into the much more important institution we have named. At the Restoration, Dr. Wilkins, who had retained the appointment of master of his college after his marriage, contrary to the statutes and by a dispensation from Cromwell, was, of course ejected, and, coming to London, his fortune was for some time at the lowest ebb, for he was out of favor both at court and at Lambeth, and could hardly expect much preferment. He did not, however, for this reason slacken in the pursuit of what then passed for natural philosophy, but continued to communicate on such subjects with his scientific friends. He also formed one of a party who met at Gresham College, first, to hear the lectures there given, and afterwards for "mutual converse," every Wednesday afternoon during term time at three o'clock, "where, amongst other matters that were discoursed of, something was offered about a design of founding a college for the promoting of physico-mathematical experimental learning." "There arose at this time," as Dr. Whe- | biographer, that in the exercise of his imwell observes, "a group of philosophers, portant functions in the latter part of his who began to knock at the door where truth was to be found, although it was left for Newton to force it open." These earnest and honest men were the actual founders of the Royal Society, and among the foremost of them stands the Reverend Mr. Wilkins. It was while thus occupied that our philosopher received the appointment of preacher at Gray's Inn. His affairs and finances being thereby improved, and his position in London established, he presided on the 28th November, 1660, over a remarkable meeting, at which it was finally decided to form a society for the pursuit of natural knowledge. This society having shortly afterwards been mentioned to the king, his approval and encouragement were obtained, and, being announced on the following 5th December, the Royal Society may be said to have been from that time established. ence. The chairman of a meeting at which so remarkable a body received life must ever be regarded as a personage in English sciBut he was also a remarkable man in himself, for in spite of his puritanical opinions and his intermarriage with the family of the arch-rebel, he contrived to put himself on good terms both with the political and ecclesiastical authorities after the Restoration. Thus, in 1662, when the first charter of the Royal Society was granted by King Charles the Second, we find among those mentioned as members of the first " and modern" council of twenty-one, to whom was devolved the important duty of selecting the first fellows of the society, Robert Boyle, Kenelm Digby, William Petty, Christopher Wren, and others, with " John Wilkins, Doctor of Divinity," as worthy associates for so worthy a purpose, the object of the society being "to confer about the hidden causes of things, with a design to establish certain and correct uncertain theories in philosophy, and by their labors in the disquisition of nature to prove themselves real benefactors to mankind." In the year preceding that in which the charter was granted to the Royal Society, Dr. Wilkins had been presented to a living in the city in the gift of the crown, and soon afterwards he was promoted to the deanery of Ripon. In 1668, he was appointed to the bishopric of Chester, and, we are told by his career (which terminated in 1672) " he filled his episcopal office with a goodness answerable to the rest of his life, but with a prudence above it, considering the two extremes of popery and fanaticism, which were nowhere then so much as in his diocese." Turning now to consider the scientific dreams and discoveries of Dr. Wilkins, we begin with a work published in 1638, entitled A Discovery of a New World; or, a Discourse tending to prove that it is probable there may be another Habitable World in the Moon: with a Discourse concerning the Possibility of a Passage thither. This idea of the moon being inhabited was not then new, and has not quite passed out of date. While at one time we are told that the absence of atmosphere and water would render life on it impossible, at another time astronomers suggest the possibility of vapor and atmosphere different, perhaps, from that to which we are accustomed, but by no means incapable of supporting a mooncalf. As to the passage thither, indeed, no practicable means have ever been suggested, for although the author of the tract before us believes that the earth's attraction, supposed by him to be a kind of magnetism, might be overcome in various ways mechanically, more complete knowledge of the nature of the force of gravitation has added greatly to the improbability that we can ever move ourselves beyond its local influence. This, therefore, is a prophecy unaccomplished, and is likely to remain so. A year or two after the publication of the essay just referred to, Wilkins published a treatise entitled Mercury; or, the Swift and Sure Messenger: showing how a Man may, with Privacy and Speed, communicate his Thoughts to a Friend at any Distance. Concerning this book the following doggerel lines of a certain Richard West, who edited a second edition some years afterwards, will serve to give a general notion. He tells us that not only are we to learn the way of attaining perfect secrecy in communication, but "Our thoughts will now arrive before they're stale: They shall no more wait on carrier's ale run. of "a flying chariot than which imagination itself cannot conceive any one more useful, since by this means a man may have as free a passage as a bird, which is not hindered by the highest walls, or the deepest rivers and trenches, or the most watchful sentinels." It is true that the notion of sailing through the air like birds is of very ancient date, and that Roger Bacon states that he has heard of a machine to accomplish this purpose. But it seems certain that no human being ever actually ascended far into the air in any floating balloon till, in 1783, the broth made useful, except on a small scale, in war, but that is because they cannot yet be guided. When this is secured the prophetic description will be perfect. Writing's an act of emanation, And thoughts speed quick and far as day doth ers Montgolfier made their first successful experiment near Lyons, in France. It would Doggerel indeed! Marvellous revelations be difficult, however, to find words to exwould be expected from such an announce-press in smaller space, or with greater refment; and, although the first glance at the erence to the modern contrivances of balbook suggests a notion that the secrets thus loons, all that these machines can perform, trumpeted are somewhat shabby and lean, than those made use of in the above short there are some exceedingly singular sugges-extract. Balloons, indeed, have not yet been tions mixed up with odd and apparently unmeaning matter. The art of secret information generally is defined and set forth in great minuteness of detail, and with a distinct Greek and Latin nomenclature worthy On the subject of rapid communication of of a new science. It includes three branches: news generally, we find in this same work a the first of which is a kind of arranged non-reference to "three saturnine angels and sense-talk, made up of broken words, and corresponds well with the peculiar jargon that school-children have adopted from time immemorial when discussing their affairs with favorite companions. The second department includes the formation and use of cypher alphabets, often invented and modified with great ingenuity, but always capable of being made out when there is any real necessity for doing so. The third method is a kind of short-hand, but the key to this, like that of cyphers, and also like that of many written languages almost lost, can be with singular ease discovered, owing to the much greater abundance of certain letters and words in every language than others, and an invariable and inevitable law thus obtained. All these methods or departments of secret communication, curious and ingenious enough at the time, may now be said to have little value, and possess no general interest. While, however, describing these familiar and not very useful secrets, our author suggests others far less probable, as it might seem at the time, but which have been found more useful and practicable. Thus he speaks certain images by which in the space of twenty-four hours a man may be informed of news from any part of the world." If the saturnine angels or messengers be translated to mean metallic wires, and the images the dial-plates of telegraphic instruments, all that is apparent in the electric telegraph would be described, but as the nature of the power or influence is not alluded to, the hint is hardly sufficient. Much more distinct, however, is the sentence that follows shortly after, when "certain fabulous relations that concern secret and swift conveyances," are thus described. "Let there be two needles provided of an equal length and business, being both of them touched with the same loadstone. Let the letters of the alphabet be placed in the circles on which they are moved, as the points of the compass under the needle of the mariner's chart. Let the friend that is to travel take one of them with him, first agreeing upon the days and hours wherein they should confer together, at which times, if one of them move the needle of his instrument to any letter of the alphabet, the other needle, by a sympathy, will move unto the same letter in the other instrument, though they be never so far distant. And thus, by several motions of the needle to the letters they may easily make up any words or sense which they have a mind to express." the useful conclusion that we frequently meet with, and the suggestions that abound in their works. Step by step knowledge has advanced; one after another the various sciences and departments of science have taken their natural place in the great series. At one time minute accuracy of detail, and at another broad generalizations, have marked the advance, but those have not been the least valuable friends to scientific research who have collected the facts and suggested the practical applications that might possibly result from them. There was something of prophecy even in the scientific dreams of Dr. Wilkins, because he loved truth, and pursued science for its own sake. The difference between the habit of thought in such a man two centuries ago and at the present time is not greater than the difference that exists between the early and later memoirs published in the Transactions of that learned body of which Dr. Wilkins was a founder. Bishop Wilkins set forth their ideal views of what science is doing or will do. Although what they wrote seems to us now so unpractical, we must not conclude that men of this stamp were without wisdom and honesty, or Dr. Wilkins, while he thus describes what that they did not exert themselves to the he was informed could be done, evidently utmost, according to their knowledge and has grave doubts as to its possibility. He ob- powers, for the improvement and enlightenserves, first," that every natural agent is sup- ment of mankind. They had but few facts posed to have some certain sphere, which de- to work upon, and little experience of accutermines its activity," and therefore that this curate observers to fall back upon. Every sympathy between distant magnets was im- thing around them was equally new and probable. Secondly, he says, that " mag-wonderful, and if they had not generalized netical operations do not arise from mere by instinct they never could have arrived at sympathy, but from such a diffusion of these magnetical qualities through the medium that they may be continued from the agent to the patient." Still he describes and refers to it as to a fact, and it is not a little curious to see in this suggestion of a result only recently attained, how completely the imagination has gone ahead of the observing and reflective faculties. The principle involved in all practical telegraphic operations, that of making soft iron magnetic by passing through it a galvanic current, and the facility thus obtained of making and unmaking a magnet at will is not referred to in these speculations, and is altogether a modern invention. The communication of magnetic currents by metallic wires, although exceedingly useful and generally adopted, is not so essential, and thus one very small step, and one only, really separates this suggestion, doubtful even to the suggestor, from the marvellous realization of our own day. There is something exceedingly interesting in looking back to the infancy of science and tracing the foreshadowing of great inventions in the mind of an ingenious man, whose imaginative and poetic intellect was enabled to overleap the mechanical difficulties that for centuries prevented the successful carrying out into practice of the ideas he entertained. It may be very doubtful whether such guesses and vague fancies really assist the more matter-of-fact discoverer in after times, but there is no doubt that they prepare the minds of men, and keep alive an excitement which may often tend in its operation to promote discovery. From The London Review. HOW TO BURN POWDER. WE had occasion, a few weeks ago, to lay before our readers an account of some ingenious experiments by means of which Captain Rodman, of the Ordnance Department of the United States, had ascertained the varying amounts of pressure in different parts of a cannon during the act of discharge. He found that when ordinary small-grained powder is burned in a cannon the combustion is so rapid, and the gases are consequently so quickly developed and so highly heated, that an enormous pressure is produced at the breech of the gun before the ball starts from its seat; then, as the gases expand the pressure is rapidly reduced, so that the velocity of the ball is small in proportion to the maximum pressure exerted upon the gun. It occurred to him upon ascertaining this fact, that if the powder were made to burn a little more slowly, the pressure would be less at the breech, and would follow up the ball with more force during its passage out of the gun, thus giving greater velocity to the shot, with less danger of bursting the cannon. He accordingly attempted to produce a slower combustion by making the powder in large grains, which were compressed with great force so that they could not be permeated by the gas, but must burn only by gradual combustion commencing from the outside and extending inwards. Powder was accordingly procured of the same quality, except in the size of the grains, which were in one sample three-tenths of an inch in size, in another five-tenths, and in the last six-tenths. These were experimented with in an 11-inch gun, using the same weight of charge and of shot at every fire. The results are given in a tabulated form in his official report. They prove at a glance that the pressure in his gun is more equalized, and the actual velocity of the shot increased as the diameter of the grains becomes larger. The smallest grained powder, three-tenths of an inch in size, produced a pressure at the bottom of the bore of thirtyfive thousand pounds to the square inch, which was reduced to sixty-seven hundred pounds, at twenty-eight inches from the bottom of bore, giving an actual velocity to the shot of only eight hundred and ninety feet per second; whilst the powder of largest grain, six-tenths of an inch in size, though producing a pressure of only twenty-one thousand pounds at the bottom of the bore, followed it up with eight thousand pounds at twenty-eight inches, and gave a velocity to the shot of nine hundred and thirty-three feet per second. A little theoretical reasoning upon the results thus obtained shows that the granular form of powder is not the best for ordnance purposes, whatever be the size of the grains employed. In order to give the greatest possible velocity to the shot with such degree of pressure as may be safely employed, the pressure against the shot should continue nearly uniform throughout its passage from the gun; and as the shot starts very slowly at the breech, and moves with a constantly accelerated velocity along the bore, it is necessary, in order to make the pressure uniform throughout, that the gases should be evolved from the burning powder with a corresponding acceleration. With granular powder, however, the combustion commences on the surface of the grains, and proceeds inwards; the size of the grains and the extent of burning surface is constantly being reduced, and consequently the rapidity with which the gases are evolved is retarded instead of being accelerated. Captain Rodman, therefore, devised a form of cake powder, in which the burning surface was constantly being enlarged instead of reduced, the pressure of gas increasing in the same ratio. A cylinder of exactly the same size as the bore of the gun is furnished with a piston; slightly damp powder is placed into this, and it is moulded into a cake by means of powerful pressure applied to the top of the piston. This latter is armed with steel rods at equal distances over its surface, and of the same length that the cake is required to be thick; by means of these the cakes of powder are pressed into shape, and are perforated with cylindrical holes at the same time. Each cake is from one to two inches thick, and is made of such a size and shape that it will exactly fit the bore of the gun. The combustion in this case will be wholly from the insides of the hollow tubes through the cake, and the increasing rapidity of the evolution of gas may be regulated so as to give any desired pressure along the bore by establishing the proper relation between the number and diameter of the cylindrical holes and the thickness of the walls between them. The thickness of the walls should be such as to be burned through by the time the projectile has nearly traversed the length of the bore, allowing the gas to act expansively during the remainder of the distance. It will be readily seen from the foregoing that this form of cake powder gives us entire control over the rate of combustion of the charge, a fact the importance of which can hardly be overrated. Our own government has lately been moving gradually in the right direction by increasing the size of the grains of powder used in heavy ordnance; and we now understand that one of our most |