elsewhere, depends on the power of the electric current to render soft iron a temporary magnet. Such a magnet is made to act on a lever, that regulates the motion of a pencil, under which a slip of paper travels with a regulated velocity guided by clock-work. When the current is set on, the pencil presses on the paper; when it is interrupted, the pencil is raised. It is evident that a succession of dots, lines, and intervening blank spaces, of any length, may thus be formed at pleasure; and these can be interpreted according to the conventional meaning attached to them.

In the electro-chemical telegraph of Mr Bain, a metallic point is made to travel on a sheet of paper moistened with a chemical solution. When contact is made, the current passes from the point through the moist paper to the metal plate on which it lies, and in passing decomposes the chemical solution, leaving a coloured spot. If the current is maintained, a line is traced; and thus dots, lines, and blanks may be produced in coloured ink, as it were. With this system, according to Dr Lardner, 20,000 words can be sent 1000 miles in an hour.

The galvanic principle has also been applied to the movement and regulation of clocks. (See HOROLOGY.)

MAGNETO-ELECTRICITY.

Magneto-electricity is the counterpart of electromagnetism: the one explains the production of magnetism by an electric current; the other shews how an electric current may be produced from a magnet. This branch of the science was created by Professor Faraday.

Since a helix charged with a current can magnetise a bar lying in it, if we take a bar-magnet and put it into a coil which has no connection with a voltaic circuit, we should naturally expect an electrical current; but no current is observed. Let us, however, seize hold of the magnet, and instead of its lying at rest in the hollow of the coil, let it be moved backwards or forwards; a current is immediately produced, the needle of the electrometer being sensibly deflected. The electricity arising from this action is called Magneto-electricity.

If an active wire, in connection with a circuit, lies alongside of another wire that is inactive and connected with a galvanometer, the current of the first has no influence in making a current in the second while both wires are at rest; but at the instant the current is arrested, and the instant that it is set on upon the first wire, a momentary current appears on the second. While the current continues, there is no action. Let, however, the wires be made to approach each other, and a current ensues on the inactive wire; when the wires are at a stand-still, it ceases. Or if they are drawn away from each other, a current in like manner arises, but opposite to the current during the approach: so that there are two methods of passing a current from an active to an inactive circle. We may either close or break the active either close or break the active circle, and thereby create an instantaneous current; or we may move the wires nearer or further from each other, and during either motion we have a current on the inactive circle; the approach making it in one direction, the recession making it in the opposite direction. These effects are designated by the term Volta-electric Induction; and the currents, Induction Currents.

The approximation or separation of the wires is exactly similar to the moving of the magnet in the coil, or across a wire. An active wire is a magnet, and if it is moved sideways towards another wire, the effect is the saine as if a magnetic bar were moved endways. The side motion of the one, can do exactly what the longitudinal motion of the other can do. In both cases, mere proximity has no effect; but, by movement, each can excite a current in a dead circle.

By making a plate of copper revolve with its edge

between the poles of a magnet, Faraday was able to produce a permanent electric current. The shock given by an induced magneto-electric current is more severe than that of a primary current. Magneto-electric machines for medical purposes are contrived so as to give the current a character of rapid intermission, which increases its effect.

ELECTRICITY OF ANIMALS AND VEGETABLES. The most striking case of electricity produced by animals, is that of certain fishes, of which the Torpedo and Gymnotus Electricus, or electrical eel, are the most remarkable. These animals have special organs, of a large size, consisting of a number of cells, in which the electricity is generated as in a galvanic pile, but by what particular action is not understood. The upper side of the torpedo is positive, and the under negative, and the discharge is sent from the one to the other through the surrounding water, and whatever conductor intervenes. The discharge seems under the control of the will, and the animal by repeated shocks can stun its enemies and its prey.

But apart from the possession of special organs, the vital functions generally seem to be attended by the development of electricity. It has been proved by Matteucci and others, that both in living animals and in those recently killed, there is always a current circulating from the interior of a muscle to its surface. In this way, by placing a number of half thighs of frogs one upon another, is formed a muscular pile, capable of producing sensible effects. The surface of the human body is generally in a positive condition; but fatigue, exhaustion, and cold are said to produce a negative condition.

The effects of a voltaic current sent through the nerves are remarkable. It produces contractions of the muscles, and convulsive motions of the limbs. The bodies of mer and animals recently deprived of life, are thus thrown into a state of violent activity resembling life. Suspended animation has thus occasionally been restored. When the current traverses any part of the optic nerve, a sensation of light is produced; similarly, the effect on the nerves of hearing is to excite the sensation of sound and so with the other senses.

If a current continue to pass along a motor nerve for some time, the nerve loses its excitability; but this is restored by reversing the current. The chief effect is always produced at the beginning and end of the contact. From these and similar facts, it was not unnatural to suppose that the nerve-force, or nervous energy, may be nothing else than an electric current. Careful examination, however, disproves this; no indications of an electrical current can be detected in the nerves of living animals, nor indeed does the arrangement seem to admit of it, there being no appearance of a closed circuit. But though not identical, the two forces are analogous, and intimately related, similarly to heat and electricity. 'The development of electricity by a crystal of tourmaline when heated, clearly proves the relation between heat and electricity: a similar relation between the nervous force and electricity is demonstrated by electric fishes. Electricity is not, however, the nervous force, any more than heat is electricity: the one changes into the other in the one case, by the form of the integrant molecules of the crystal; and in the other, by the structure of the electric organs.'

Recent researches would seem to establish the fact, that the process of vegetation also excites abundance of electricity. Carrents are said to be detected in all parts of vegetables. The result of one set of experiments is, that the roots and all the interior parts of the plants filled with sap, are permanently negative, while the moist surfaces of the fresh branches, leaves, &c., are permanently positive. It is not unlikely that vegetation thus exercises a powerful influence on the electrical condition of the atmosphere.

with the solar or natural day, which is that portion of time elapsing between the arrival of the sun at the meridian, or mid-day, on two consecutive days. The mean length of this period of time is twenty-four hours; nearly 3 minutes 56 seconds on the average being required, in consequence of the earth's motion in its orbit, to bring the sun up to the same meridian on every successive day. The inclination of the plane of the earth's equator to the plane of its orbit, however, and the unequal rapidity of the motion of the earth in its orbit, really cause the solar or natural days to be of unequal length; so that, though averaging twenty-four hours each, they sometimes fall short, and sometimes exceed that average. (See ASTRONOMY.)

We have thus three species of day-the sidereal, or that time which elapses between two successive culminations of the same star, and which is now universally adopted by astronomers in their observatories; the solar, natural, or apparent day, being the time that elapses between two consecutive returns of the same terrestrial meridian to the centre of the sun, and which consequently commences at noon; and the civil or mean solar day, which is the mean or average of these meridional returns, and which most modern nations have adopted, placing the commencement and termination at mean midnight.

It is here necessary to observe, that as the earth rotates from west to east, every meridian has its own natural day; and any place east or west of that meridian has a corresponding earlier or later sunrise. The earth, of 360° of longitude, turns in twenty-four hours; consequently every hour is equal to 15°; and every degree equal to four minutes of time. Thus, taking Greenwich as the normal meridian, Alexandria being 30° east, is two hours earlier, or has it twelve o'clock when it is ten at Greenwich; Bengal is 90° east, and it is there twelve at noon when only six in the morning at Greenwich. So New York is 74° west, or 4 hours 56 minutes; and consequently, when noon at Greenwich, it is only four minutes past seven in the morning at New York. As with these large distances, so with every other difference of longitude, however minute; and it is thus that we speak of our clocks being earlier or later than Greenwich time, according as we are situated east or west of that meridian. Ipswich, for example, being east of Greenwich, is about five minutes before, or earlier; Edinburgh, being west, is about twelve and a half minutes behind; and Dublin, being still further west, is about twenty-five minutes late. Hence the necessity, in these days of rapid transit, of keeping by one uniform standard of time, or at least of having a table of differences for the principal stations throughout the country. In most cases, it would be preferable to have our clocks furnished with two minute-hands-one to indicate Greenwich time, and the other the natural time of the locality.

MONTHS AND WEEKS.

After the day, the next distinct natural measure or division of time marked out by the heavenly bodies in their time-keeping revolutions, is the month. The lunar month is the period during which the moon revolves once round the earth, and is equal to 29 days 12 hours 44 minutes 3 seconds. The solar month is the period during which the sun appears to pass through a twelfth part of his annual course, or through one of the twelve arbitrary signs of the zodiac, and is equal to 30 days 10 hours 30 minutes: it is not so distinctly pointed out by nature as the lunar month. The month came ultimately to be disconnected from the lunar and terrestrial revolutions, as will be afterwards more particularly noticed, and civil or calendar months, accommodated to the year, were substituted; these also, as well as the names given to them in their annual order, will fall to be noticed while treating of the year itself and its subdivisions.

The subdivision of the month into weeks of seven days

is very ancient, having, from the most remote period of history, been in use among the Hindoos and other nations in the East, including the Chaldeans and Jews. The week did not enter into the calendar of the Greeks, who divided the civil month into three periods, of ten days each; and it was not introduced at Rome till the time of the Emperor Theodosius. The Roman month was anciently divided into three periods-Calends, Nones, and Ides. The calends were invariably placed at the beginning of the month; the ides at the middle of the month, on the 13th or 15th; and the nones (novem, nine) were the ninth day before the ides, counting inclusively. From these three terms the days were counted backwards in the following manner :-Those days comprised between the calends and the nones were denominated days before the nones; those between the nones and ides, days before the ides; and those from the ides to the end of the month, days before the calends. The Greeks had no calends; hence the Roman phrase Græcæ calenda, or 'never,' corresponding to the English ‘Latter Lammas,' and the Scotch 'Morn come never.'

The use of weeks is supposed by some to be a remnant of the tradition of creation; by others, as suggested by the phases of the moon; while a third class refer its origin to the seven planets known in ancient times. The latter hypothesis explains the circumstance, that the days of the week have been universally named after the planets in a particular order. Thus the French, at the present day, following the practice of the ancients, name the days from Mercury, Jupiter, Venus, &c.; while the English adopt Saxon appellations, derived from the deities of Northern Europe, and from the sun and moon. Hence our term Sunday is from the Sun; Monday, the Moon; Tuesday, Tuesco; Wednesday, Woden; Thursday, Thor; Friday, Friga; and Saturday, Seater. (See SUPERSTITIONS.) In England, the Latin names of the days are still retained in legislative and judiciary acts. The Quakers, or Society of Friends, do not use the name of the week-day, but call each day, as they do the months, by its proper number-reckoning Sunday the 1st, Monday the 2d; and so on.

YEARS AND SEASONS.

The year, properly so called, or the solar or astronomical year, is that portion of time which elapses while the sun passes through the twelve signs of the zodiac, or rather, while the earth revolves once completely round the sun in its orbit; and while, from the parallelism of the axis of the earth's rotation to itself, combined with its inclination to the axis of the orbit, each hemisphere is turned alternately, once toward, and once from the sun; thus constituting, at least in the extra-tropical regions, the distinction between summer and winter. (See ASTRONOMY.)

The distinction of the seasons would soon be found to depend upon the alternate approach and departure, or elevation and depression, of the sun in the heavens at stated and regularly recurring intervals; but the exact division of time into solar years could not have been effected till astronomy had made some progress; when it would immediately appear, in the endeavours at length made to measure the year by revolutions of the moon, that as an exact number of days, or times of the earth's rotation, is not contained in a moon,' or lunar month, so an exact number of moons, or even of days, is not contained in a year, or revolution of the seasons. Such observations as these led to methods of accommodating the one period to the other; or, in other words, to the

ADJUSTMENT OF THE CALENDAR.

The Chaldeans, Egyptians, and Indians, and indeed almost all the nations of antiquity, originally estimated the year, or the periodical return of summer and winter, by twelve lunations--a period equal to 354 days 8 hours 48 minutes 36 seconds. But the solar year is equal to 365 days 5 hours 48 minutes 49 seconds; or 10 days

21 hours 13 seconds longer than the lunar year, an excess named the epact; and, accordingly, the seasons were found rapidly to deviate from the particular months to which they at first corresponded; so that in thirty-four years, the summer months would have become the winter ones, had not this enormous aberration been corrected by the addition or intercalation of a few odd days at certain intervals. Thus was the calendar first adjusted, and the solar year estimated to consist of twelve months, comprehending 365 days. But no account was taken of the odd hours, until their accumulation forced them into notice; and a nearer approximation to the exact measurement of a year was made about forty-five years before the birth of Christ, when Julius Cæsar, being led by Sosigenes, an astronomer of his time, to believe the error to consist of exactly six hours in the year, ordained that these should be set aside, and accumulated for four years, when of course they would amount to a day of twenty-four hours, to be accordingly added to every fourth year. This was done by doubling or repeating the 24th of February; and, in order to commence aright, he ordained the first to be a 'year of confusion,' made up of fifteen months, so as to cover the ninety days which had been then lost. The Julian style' and the 'Julian era' were then commenced; and so practically useful and comparatively perfect was this mode of time-reckoning, that it prevailed generally amongst Christian nations, and remained undisturbed till the renewed accumulation of the remaining error of eleven minutes or so had amounted, in 1582 years after the birth of Christ, to ten complete days; the vernal equinox falling on the 11th instead of the 21st of March, as it did at the time of the Council of Nice, 325 years after the birth of Christ.

This shifting of days had caused great disturbances, by unfixing the times of the celebration of Easter, and hence of all the other movable feasts. And accordingly, Pope Gregory XIII., after deep study and calculation, ordained that ten days should be deducted from the year 1582, by calling what, according to the old calendar, would have been reckoned the 5th of October, the 15th of October 1582. In Spain, Portugal, and part of Italy, the pope was exactly obeyed. In France, the change took place in the same year, by calling the 10th the 20th of December. In the Low Countries, the change was from the 15th December to the 25th, but was resisted by the Protestant part of the community till the year 1700. The Catholic nations, in general, adopted the style ordained by their sovereign pontiff; but the Protestants were then too much inflamed against Catholicism in all its relations, to receive even a purely scientific improvement from such hands. The Lutherans of Germany, Switzerland, and, as already mentioned, of the Low Countries, at length gave way in 1700, when it had become necessary to omit eleven instead of ten days. A bill to this effect had been brought before the parliament of England in 1585, but does not appear to have gone beyond a second reading in the House of Lords. It was not till 1751, and after great inconvenience had been experienced for nearly two centuries, from the difference of the reckoning, that an act was passed (24 Geo. II., 1751) for equalising the style in Great Britain and Ireland with that used in other countries of Europe. It was enacted, in the first place, that eleven days should be omitted after the 2d of September 1752, so that the ensuing day should be the 14th; and, in order to counteract a certain minute overplus of time, that the years 1800, 1900, 2100, 2200, 2300, or any other hundredth year of our Lord which shall happen in time to come, except only every fourth hundredth year of our Lord, whereof the year 2000 shall be the first, shall not be considered as leap-years.' A similar change was about the same time made in Sweden and Tuscany; and Russia is now the only country which adheres to the old style; an adherence which renders it necessary, when a letter is thence addressed to a person in

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June 26 July 9

another country, that the date should be given thus :April or for it will be observed, the year 1800, not being considered by us as a leap-year, has interjected another (or twelfth) day between old and new style.

The twelve calendar or civil months were so arranged by Julius Cæsar, while reforming the calendar, that the odd months-the first, third, fifth, and so on, should contain thirty-one days, and the even numbers thirty days, except in the case of February, which was to have thirty only in what has been improperly termed leapyear, while on other years it was assigned twenty-nine days only; a number which it retained till Augustus Cæsar deprived it of another day. The names of the twelve months are strictly Roman :-Thus, January is said to be derived from Janus, a divinity who presided over the commencement of all undertakings, whence his name was appropriately applied to the first month in the year; February, from februo, 'I purify,' because in that month funeral lustrations were performed at Rome; March, from Mars, the reputed father of Romulus; April, probably from aperire, to open,' in allusion to the opening or budding of vegetation; May, from Maia, the mother of Mercury, to whom sacrifices were offered on the first day; June, according to some, either from Junius, Juno, or Juniores; July, in honour of Julius Cæsar; August, in honour of Augustus; September, October, November, and December, signifying respectively seventh, eighth, ninth, and tenth, are the names which were employed when the Roman year consisted only of ten months, and began with March.

The commencement of the year, till a comparatively very recent period, was the subject of no general rule. The Athenians commenced it in June, the Macedonians in September, the Romans first in March, and afterwards in January, the Persians on 11th August, the Mexicans on 23d February, the Mohammedans in July, and astronomers at the vernal equinox. Amongst Christians, Christmas-day, the day of the Circumcision, the 1st of January, the day of the Conception, the 15th of March, and Easter-day, have all been used at various times, and by various nations, as the initial day of the year. Christmas-day was the ecclesiastical beginning of the year, till Pope Gregory XIII., on reforming the calendar, ordered it, in 1582, to begin thenceforward on the 1st of January. In France and England, the same practice commenced about the same time; but in the latter country, it was not till 1752 that legal writs and instruments ceased to consider the 25th of March as the beginning of the year. In Scotland, New-year's Day was altered, both for historical and legal purposes, from the 25th of March to the 1st of January, by a proclamation of King James VI., in the year 1600. The English plan was found exceedingly inconvenient; for when it was necessary to express a date between the 1st of January, which was the commencement of the historical year, and the 25th of March, which opened the legal one, error and confusion were sure to occur, unless it were given in the following awkward fashion :-January 30, 1648-9, or 1648. Even this was apt to lead to mistakes; and it is perhaps even to this day a matter of doubt with some intelligent persons, whether the execution of Charles I., of which the above is the usual appearance of the date, occurred in the year 1648 or 1649: it in reality occurred in the year which, by our present uniform mode of reckoning, would be called 1649.

The present mode of reckoning time has experienced no interruption in its leading features for many years, except under the French Republic. In September 1793, the French nation having resolved that the foundation of their new system of government should form their era, instead of the birth of Christ, whose religion they had in a great measure shaken off, resolved also that a calendar should be adopted on what was termed philosophical principles. The Convention, therefore, having

decreed, on the 24th November 1793, that the common era should be abolished in all civil affairs, and that the new French era should commence from the foundation of the Republic-namely, on the 22d September 1792, on the day of the true autumnal equinox-ordained that each year henceforth should begin at the midnight of the day on which the true autumnal equinox falls. This year they divided into twelve months of thirty days each, to which they gave descriptive names as follows:From the 22d of September to the 21st of October was Vendémiaire (Vintage Month); to the 20th November was Brumaire (Foggy Month); to the 20th December was Frimaire (Sleety Month); this completed the autumn quarter: to the 19th January was Nivose (Snowy Month); to the 18th February was Pluviose (Rainy Month); to the 20th March was Ventose (Windy Month), which completed the winter quarter: to the 19th April was Germinal (Budding Month); to the 19th May was Floréal (Flowery Month); to the 18th June was Prairial (Pasture Month); here ended the spring quarter: to the 18th July was Messidor (Harvest Month); to the 17th August was Fervidor or Thermidor (Hot Month); to the 16th September was Fructidor (Fruit Month), which terminated the period of summer. In ordinary years there are five extra days--namely, from the 17th to the 21st of our September, inclusive: these the French called Jours Complémentaires, or Sans-culottides, and held as festivals; the first being dedicated to Virtue, the second to Genius, the third to Labour, the fourth to Opinion, and the fifth to Rewards. At the end of every four years, forming what they called a Franciade, occurred a leap-year, which gave a sixth complementary day, styled Le Jour de la Révolution, and employed in renewing the national oath to live free or die.

The week, though not exclusively a Christian or Jewish period of time, they also abjured. The thirty days of the month were divided into three parts, of ten days each, called Décades; of which the first nine --called Primidi, Duodi, Tridi, Quartidi, Quintidi, Sextidi, Septidi, Octidi, Nonidi-were working or common days, while the tenth, styled Décadi, was observed as a kind of Sabbath, though not exactly in the Jewish sense of the word. The French, however, in indicating any particular day, either by word or writing, generally mentioned only the number of the day of the month. The Republican Calendar was first used on the 26th of November 1793, and was discontinued on the 31st of December 1805, when the calendar used throughout the rest of Europe was resumed.

CYCLES.

A cycle, from a Greek word signifying circle, is a perpetual round or circulating period of time, on the completion of which, certain phenomena return in the same order ; the end being thus, as it were, brought back to the beginning. Under such a definition, the common practice of accumulating years into centuries has of course no title to be classed: it is merely an arithmetical computation, like the equally common mode of counting by tens-forming, indeed, part of the same system.

The Solar Cycle is a period of twenty-eight years, during which the day of the month, in every succeeding year, falls on a different day of the week, from the first, till the cycle is completed; when the days of the month and week meet as at first, one cycle corresponding to another. By this cycle, which has no relation to the sun's course, we find the Dominical letters,' or those letters amongst the first seven in the alphabet-used to represent the days of the week-which point out the days of the month on which the Sundays fall during each year of the cycle. If there were 364 days in the year, the Sundays would happen every year on the same days of the month; if 365 exactly, every seventh year; but because the additional fractional period

contained in the year makes an alteration of a day in every fourth year, the cycle extends to four times seven, or twenty-eight years.

The first solar cycle in the Christian era having begun nine years before the commencement of that era, to discover what year of the cycle the year 1856 forms, we must add 9, and divide the sum 1865 by 28, the period of the cycle, and the quotient 66 is the number of solar cycles that have passed during that era, the remaining 17 being the year of the cycle corresponding to 1856.

The Lunar Cycle-also called the Golden Number,' from its having been written in letters of gold by the Greeks, and the 'Metonic Cycle,' from its having been discovered by Meton, an Athenian astronomer-is a period of nineteen years, at the end of which the phases of the moon occur on the same days of the civil month as in a previous lunar cycle, and within an hour and a half of the same precise moment of time.

The first lunar cycle in the Christian era having begun one year before the commencement of that era, to discover what year of the cycle 1856 forms, we must add 1, and divide the sum 1857 by 19, the period of the cycle, and the quotient 97 is the number of lunar cycles that have passed during that era: the remainder, 14, shewing that 1856 is the fourteenth year of the next lunar cycle.

The Dionysian Period is a combination of the solar and lunar cycles, forming, by the multiplication of 28 by 19, a period of 532 years, at the expiration of which it is again new moon on the same days of the week and month as before: chronological events are compared and tested by such a calculation.

The Indiction may here also be noticed; though, were it not for severing it from the other cycles with which it is connected in the Julian period, it might perhaps more properly appear under the head of epochs and eras. This was a Roman period of fifteen years, the first of which commenced in the year 312 after the birth of Christ. It was appointed merely for the regulation of certain payments by the subjects of the empire; but it came to be observed by the Greek Church and the Venetian senate, as well as the court of Rome.

The Julian Period is a combination of the solar and lunar cycles with the Indiction; the respective periods of 28, 19, and 15 years being multiplied by each other, and the product, 7980 years, being what is called the Julian period, during which there cannot be two years having the same numbers for the three cycles; but at the termination of this period they return in the former order.

The year 1856 is the 6569th of the Julian period : hence it began about 700 years previous to the date vulgarly assigned to the creation of the world, and has been used instead of that era, to obviate the disputes of chronologers, and to reconcile their systems; for all agree as to the year in which the Julian period began.

The Precession of the Equinoxes, on the supposition that the motion on which it depends is uniform, is a cycle of 25,868 years, during which the points whereat the sun crosses the equator at the equinoxes retrograde along the whole circle of the ecliptic, and return to their former position. The present rate of this motion, which depends on the solar and lunar attraction of the quantity of matter heaped up along the region of the equator, is fifty seconds of a degree yearly, or a whole degree in seventy-six years. (See ASTRONOMY.)

Sir Isaac Newton endeavoured to fix the period of the Argonautic expedition by this cycle, and it has given rise to some curious and interesting speculations regarding the period when the signs of the zodiac were invented.

EPOCHS AND ERAS.

The principal difficulty which must have presented itself to nations desirous of preserving the memory of