think him too highly rewarded, if it be true that his cotton is so much more powerful than that of his competitors, as his friends represent it to be. The man who invents the most rapid and the most effectual means of destruction, as regards war, is the greatest friend to the interests of humanity. Before gunpowder was invented war was a very favourite pastime of the rulers of nations, for it served to gratify their bad passions without presenting the chances of utter ruin to them. By risking a portion of the money derived from the labour of their subjects, and sacrificing a few hundred lives, they were able to play at the game of ambition; and, having always the hope of success before them, they had a constant excitement to violence and outrage. Nor did the pastime cease with the invention of gunpowder. The scale on which it was carried on was greater; but in a few years, when military tactics had been improved, and fire-arms had been made on surer principles, the game became too hot for the gamesters, and they were glad to retreat at length from the struggle of vain glory. The bow and arrow work of the ancients was nothing more than child's play to the fields of Austerlitz and Waterloo; and, when once a suspension of hostilities had taken place, governments began to reflect that the game was too costly. Thirty years of peace have served to give birth to better ideas; but there is every now and then an indication of a desire to involve nations in warfare. We are quite sure, however, that if any man could invent a means of destruction, by which two nations going to war with each other would see large armies destroyed, and immense treasure wasted, on both sides, in a single campaign, they would both hesitate at entering upon another. We repeat, therefore, that in this sense the greatest destroyer is the greatest philanthropist; and supposing what is said of M. Schonbein's invention to be true, we think that all governments will, in the event of differences, try all possible means of concession and conciliation before coming to a trial of strength in

which the strong as well as the comparatively weak must be such great losers."

No better result could have been desired, and as the world grows wiser the truth of these assertions will be not only readily recognised, but acted on. The governments of England and France have both declined to use the "gun-cotton," as it is called, instead of gunpowder, because it is alleged that it explodes with such a small degree of heat, that after a few discharges a musket would be so hot as to go off the moment the charge was put within the barrel.

The invention is not, however, quite so new in principle as was generally supposed, for at the same meeting of the academy to which we have alluded, M. Pelousi, one of the members, said, "Although M. Schonbein has not published the nature or mode of preparation of his cotton, it is evident that the properties which he assigns to it can only apply to xyloidine. M. Dumas, as well as myself, made this remark in the origin of the first communications of M. Schonbein. Reasoning on the hypothesis that the poudre coton is nothing else than xyloidine, I may be permitted to say a few words. with respect to its history, and some of its properties. Xyloidine was discovered in 1833 by M. Braconnet, of Nancy. He prepared it by dissolving starch and some other organic substances in nitric acid, and precipitating these solutions in water. In a note inserted in the Comptes rendûs de l' Academie des Sciences, in 1833, I showed that the xyloidine resulted from the union of the elements of the nitric acid with those of starch, and explained, by this composition, the excessive combustibility of the substance produced. I ascertained and this I think is a very important result in the history of the applications of xyloidine—that, instead of preparing it by dissolving the cellulose, it might be obtained. with infinitely greater facility and economy by simply impregnating with concentrated nitric acid, paper, cotton, and

hemp, and that these organic matters thus treated took fire at 180 degrees, and burnt almost without residuum, and with excessive energy; but I think it right to add, that I never for an instant had an idea of their use as a substitute for gunpowder. The merit of this application belongs entirely to M. Schonbein. Eight years ago, however, I prepared an inflammable paper by plunging it into concentrated nitric acid. After leaving it there for twenty minutes I washed it in a large quantity of water, and dried it in a gentle heat. I have recently tried this paper in a pistol, and with about three grains. pierced a plank two centimetres in thickness (about three quarters of an inch) at a distance of twenty-five metres."

M. Otto, of Brunswick, Dr. Knapp, of Berlin, Mr. Taylor, of London, Mr. Phillips, of Brighton, and several other individuals connected with science, have produced similar results, not only from cotton, but from other vegetable products. The full effects of this discovery have not yet been ascertained, though its manufacture in this country is likely to be very extensive for both sporting and mining purposes. The history of explosive substances, so far as our present experience extends, may here be said to terminate. This review of them teaches us at least one truth, that mental exertion, especially when employed in scientific investigation, will always prove superior to brute force, no matter how skilfully directed.

CLOCKS.

HE measurement of Time must have been an art which the earliest of mankind were desirous of discovering. No accurate account of events could be transmitted to their posterity without it; and when human society began to take an orderly form, this division of time became the more necessary for the regular performance of social duties and labours. The "lights in the firmament of the heaven were not only to divide the day from the night, but were to be "for signs, and for seasons, and for days, and for years." The regulation of the "seasons" men beheld to be evidently dependent on the sun; and their periodical return began to be classed as comprising a "year."

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The day," or period between the apparent rising and setting of the sun, or, as inclusive of night, the period from sun-rise to sun-rise, would afford a ready means of enabling the first men to apply their rude science of numbers to the length of a year. The moon, by its succession of phases in twentyeight days, afforded an easy reference for the subdivision of months; while the fourth of this period dictated the further subdivision of weeks, common to all the early nations.

Our own island-king, Alfred the Great, had no clock with which to measure out time, only the sun and shadow to divide the hours, both useless in the dull cloudy day and amid the darkness of night. To overcome this difficulty, and divide the night and day into twenty-four portions, he made wax candles,

twelve inches in length, and each of these he marked at equal distances; and, although the time occupied in replacing and relighting them would scarcely serve to mark the lapse of minutes accurately, yet they were so equally made, that six of them, used in succession, with but little variation, burnt through the twenty-four hours. To guard against the casualties of winds and draughts, he enclosed these candles in thin white transparent horn, and this led to the invention of lanterns. It was several centuries after the death of this great king before. clocks were discovered.

The division of the day into hours was fixed at the number twenty-four, from the earliest date of authentic history; but the means of determining the hours, with such further subdivisions as would soon be found necessary, were at first very imperfect.

The sun-dial was in use among the earliest nations. Herodotus says that the Greeks borrowed it from the Babylonians. The art of Dialling, or Gnomonics, was, up to the end of the seventeenth century, considered a necessary part of a mathematical course; it will, now, be sufficient to explain familiarly the principles on which dials are constructed.

If a person were to place a staff in the ground, so as to point either vertically or otherwise, and to watch its shadow at the same hour, on different days at some intervals from each other, marking its direction at each day's observation, he would, in all probability, find that the direction of the shadow, the hour being always the same, varied from day to day. He might, however, find that the shadow was always in one direction at the same hour, and this might happen in two different ways. First, he might by accident fix the staff in a direction parallel to that of the earth's axis, in which case the direction of the shadow would always be the same at the same hour, at all times of the year, and for every hour. Secondly, having fixed the staff in a position not parallel to the axis of the earth,