Measurement of Time.

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of London, it is almost one o'clock when it is twelve at London.

Time, like bodies, is divisible nearly ad infinitum. A second (a mere pulsation) is divided into four or five parts, marked by the vibrations of a watch-balance; and each of these divisions is frequently required to be lessened an exact 2880th part of its momentary duration. It is, however, impossible to see this; for Mr. Babbage, speaking of a piece of mechanism which indicated the 300th part of a second, tells us that both himself and friend endeavoured to stop it twenty times successively at the same point, but could not be confident of even the 20th part of a second.

It has been said that many simple operations would astonish us, did we but know enough to be so; and this remark may not be inapplicable to those who, having a watch losing half a minute per day, wish it corrected, though they may not reflect that as half a minute is the 2880th part of 24 hours, each vibration of the balance, which is only the fifth part of a second, must be accelerated the 2880th part of its instantaneous duration; while to make a watch, losing one minute per week, go correctly, each vibration must be accelerated the 1008th part of its duration, or the 50,400th part of a second.*

Among the early methods of measuring Time, we must not omit to notice Alfred's "Time-Candles,” as they have been called. His reputed biographer, Asser, tells us that Alfred caused six tapers to be made for his daily use: each taper, containing twelve pennyweights of wax, was twelve inches long, and of proportionate breadth. The whole length was divided into twelve parts, or inches, of which three would burn for one hour, so that each taper would be consumed in four hours; and the six tapers, being lighted one after the other, lasted twenty-four hours. But the wind blowing through the windows and doors and chinks of the walls of the chapel, or through the cloth of his tent, in which they were burning, wasted these tapers, and consequently they burnt with no regularity; he therefore designed a lantern made of ox or cow horn, cut into thin plates, in which he enclosed the tapers; and thus protecting them from the wind, the period of their burning Time and Timekeepers. By Adam Thomson, 1842.

became a matter of certainty. But the genuineness of Asser's work is doubted, so the story is discredited. Nevertheless, there is nothing very questionable in Alfred's reputed method; and it is curious to see that an "improvement" was patented so recently as 1859, which consists in graduating the exterior of candles, either by indentation or colouring at intervals, and equal distances apart, according to the size of the candles. The marks are to consist of hours, half-hours, and, if necessary, quarter-hours; the distance to be determined by the kind of candle used.

Bishop Wilkins, in his Mathematical Magic, in the chapter relating to "such engines as did receive a regular and lasting motion from something belonging to their own frame, whether weights or springs, &c.," quotes Pancirollus, "taken from that experiment in the multiplication of wheels mentioned in Vitruvius, where he speaks of an instrument whereby a man may know how many miles or paces he doth go in any space of time, whether or no he pass by water in a boat or ship, or by land in a chariot or coach. They have been contrived also into little pocket instruments, by which, after a man hath walked a whole day together, he may easily know how many steps he hath taken." More curious is "the alarum, mentioned by Walchius, which, though it were but two or three inches big, yet would both wake a man and of itself light a candle for him at any set hour of the night. And those great springs, which are of so great force as to turn a mill (as some have contrived), may be easily applied to more various and difficult labours."

Occasionally, in these old curiosities, we trace anticipations of some of the scientific marvels of the present day. Thus, when the Grand Duke of Tuscany, in 1669, visited the Royal Society at Arundel House, he was shown “a clock, whose movements are derived from the vicinity of a loadstone; and it is so adjusted as to discover the distance of countries, at sea, by the longitude.” The analogy between this clock and the electrical clock of the present day is not a little remarkable. The Journal-book of the Society for 1669 contains many allusions to "Hook's magnetic watch going slower or faster according to the greater or less distance of the loadstone, and so moving regularly in every posture."

On the occasion of the visit of illustrious strangers, this clock and Hook's magnetic watches were always exhibited as great curiosities.*

PERIODS OF REST.

The terrestrial day, and consequently the length of the cycle of light and darkness, being what it is, we find various parts of the constitution both of animals and vegetables which have a periodical character in their functions, corresponding to the diurnal succession of external conditions; and we find that the length of the period, as it exists in their constitution, coincides with the length of the natural day.

Man, in all nations and ages, takes his principal rest once in twenty-four hours; and the regularity of this practice seems most suitable to his health, though the duration of the time allotted to repose is extremely different in different cases. So far as we can judge, this period is of a length beneficial to the human frame, independently of the effect of external agents. In the voyages made into high northern latitudes, where the sun did not rise for three months, the crews of the ships were made to adhere, with the utmost punctuality, to the habit of retiring to rest at nine, and rising a quarter before six; and they enjoyed, under circumstances apparently the most trying, a state of salubrity quite remarkable. This shows that, according to the common constitution of such men, the cycle of twentyfours is very commodious, though not imposed on them by external circumstances.

The succession of exertion and repose in the muscular system, of excited and dormant sensibility in the nervous, appears to be fundamentally connected with the muscular and nervous powers, whatever the nature of these may be. The necessity of these alternations is one of the measures of the intensity of these vital energies; and it would seem that we cannot, without assuming the human powers to be altered, suppose the intervals of tranquillity which they require to be much changed. This view agrees with the opinion of the most eminent physiologists. Thus, Cabanis notices the periodical and isochronous character of the desire

* See Weld's History of the Royal Society, vol. i. pp. 220, 221.

of sleep, as well as of other appetites. He states that sleep is more easy and more salutary, in proportion as we go to rest and rise every day at the same hours; and observes that this periodicity seems to have a reference to the motions of the solar system.

Now, how should such a reference be at first established in the constitution of man, animals, and plants, and transmitted from one generation of them to another? If we suppose a wise and benevolent Creator, by whom all the parts of nature were fitted to their uses and to each other, this is what we might expect and understand. On any other supposition, such a fact appears altogether incredible and inconceivable.*

RECKONING DISTANCE BY TIME.

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In Oriental countries, it has been the custom from the earliest ages to reckon distances by time, rather than by any direct reference to a standard of measure, as is commonly reckoned in the present day. In the Scriptures we find distances described by " a day's journey," three days' journey,' and other similar expressions. A day's journey is supposed to have been equal to about thirty-three British statute miles, and denoted the distance that could be performed without any extraordinary fatigue by a foot-passenger; Sabbath day's journey" was peculiar to the Jews, being equal to rather less than one statute mile. It may not be in exact accordance with our habits of thought, and usual forms of expression, thus to describe distances by time; yet it seems to possess some advantages. A man knowing nothing of the linear standards of measure employed in foreign countries, would receive no satisfactory information on being told that a particular city, or town, was distant from another a certain number of milest or leagues, as the case might happen to be. But if he were told that such city or town was distant from another a certain number of hours or days, there would be something in the account that would com* Abridged from Whewell's Bridgwater Treatise.

In Holland a mile is nearly equal to three and three-quarters; in Germany it is rather more than four and a half; and in Switzerland it is about equal to five and three-quarters British miles.

A league in France is equal to two and three-quarters; in Spain to four; in Denmark to four and three-quarters; in Switzerland to five and a half; and in Sweden to six and three-quarters British miles.

Oxford and Bremhill Sun-dials.

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mend itself to his understanding. A sea-voyage is oftener described by reference to time than to distance. We frequently hear persons inquire how many weeks or months it will occupy to proceed to distant parts of the world, but they rarely manifest any great anxiety about the number of miles. This mode of computation seems especially applicable to steam navigation: a voyage by a steam-packet, under ordinary circumstances, being performed with such surprising regularity, that it might, with greater propriety, be described by minutes, or hours, or days, than by miles.

SUN-DIALS.

Sun-dials are little regarded but as curiosities in these days; although the science of constructing Sun-dials, under the name of Gnomonics, was, up to a comparatively recent period, part of a mathematical course. As long as watches were scarce, and clocks not very common, the dial was an actual time-keeper. Of the mathematical works of the seventeenth century which are found on book stalls, none are so common as those on Dialling.

Each of the old dials usually had its monitory inscription; and although the former have mostly disappeared, the mottoes have been preserved, so that all their good is not lost.

The stately city of Oxford, which Waagen declared it was worth a special journey from Germany to see, has, upon its churches and colleges, and in their lovely gardens, several dials. Christopher Wren, when a boy of fifteen at Wadham College, designed on the ceiling of a room a reflecting dial, embellished with various devices and two figures, Astronomy and Geometry, with accessories, tastefully drawn with a pen, and bearing a Latin inscription; but his more elaborate work is the large and costly dial which he erected at All Souls' College, of which he was a Fellow.

The Rev. W. Lisle Bowles was a sincere respecter of dials. In the garden of his parsonage at Bremhill he placed a Sun-dial-a small antique twisted column, gray with age, and believed to have been the dial of the abbot of Malmesbury, and counted his hours at the adjoining lodge; for it was taken from the garden of the farmhouse, which had ori

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