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MANAGEMENT OF MRS. TAYLOR.
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THE YARD MEASURE EXTENDED TO THE STARS.
BY PROFESSOR KELLAND.
As soon as astronoiny had learnt to know measured-nothing more nor less. It its position, it began to suspect that this does not concern us to enquire what earth, with its sun, and moon, and that yard-measure is. Suffice it that planets, and comets—the whole solar the legislature provide means to prevent system—is but a speck in the vast fir its fluctuation from year to year, or from mament of the heavens. The more century to century. Now, the yard can men worked and thought, the stronger readily be multiplied to a considerable grew the conviction that Sirius, the extent-for example, into a chain of little twinkling star, must be a sun, twenty-two yards—and with this chain immensely brighter than our own. For a line of three or four miles can be they had tried in vain to find out his measured on the earth's surface. The distance. In vain! The distance always yard is thus expanded into miles. It is came out infinite. The measuring line no easy matter, certainly, to measure a placed in the hand of man shrank into few miles on the surface of the earth ; nothingness in respect to the where but it is possible, and has been done. abouts of the nearest of those little orbs, An extension of this process would, of and astronomy retired abashed. Do you course, measure a very long line; but this ask me what is the measuring line is not necessary. Having once got over which man has in his hand to apply to a few miles, the yard-measure, and the the stars? I shall tell you that it is no. steel-chain, and all similar appliances small matter as men count smallness. are discarded, and the measured line It is two hundred millions of miles-a itself is assumed as a new measuring-rod. line long enough, you would think ; yet True, it cannot be carried about from this line actually shrank into nothing place to place. Mahomet cannot go to ness so absolute, that,'half a century ago, the mountain ; so the mountain must be it seemed as hopeful to mount to the brought to Mahomet. This is done by stars as to compass their distance with making direction serve as the evidence so puny a line. But the thing has been of distance. If you measure off on done at last, and triumphantly done. the paper a line a foot long, and take We know the distance of a few of the a point somewhere over the centre of it, nearest stars now, pretty accurately, at you will see how the angles of direction
And I propose to endeavour from the ends of the line depend on its to convey an idea of how this know distance from the line. So, conversely, ledge has been attained.
if a church-steeple, or some other proWell, then, to begin at the beginning, minent object, be visible from both ends the first line to which all others are re of the line measured on the earth's surferred, the primary unit, is the yard- face, its distance from either of them measure, by which ladies' dresses are can be determined at once, by means of
No. 27.-POL. V.
" units of space.
angles, without approaching the object the nations of Europe have set themat all. You see then how we can get a selves to the task. One instance degood long line of sixty or seventy miles. serves mention. Now, as the earth is a sphere or nearly In 1791-2, the National Convention so, if you travel due north a 360th of France conceived the magnificent idea part of the earth's circumference, you of establishing a new standard for everywill find that the pole star has assu thing—morals, money, and measure. med a position one degree higher in “Let the heavens," they said, “furnish the heavens. Accordingly, if you can new units of time, and the earth new measure distances and angles, the deter
Let the week, and mination of the circumference of the “the month, and the year yield up
their earth is reduced to a matter of mere "ancient prerogatives. Let the former multiplication. The old Indians had got history of the world be forgotten, and thus far; the old Greeks too. Two hun “let all history date from this time. dred and thirty years before the Christian “Let the month be divided into thirty era, Eratosthenes, the librarian of the days, and let the sabbath occur every Alexandrian library, observed the meri
Let the day be divided dian height of the sun at Alexandria, at “into ten hours, and let new dials be the time of the summer solstice, and “constructed to show them. then set to work to measure the distance girdle be drawn round the earth, which up the Nile to Syene, where the granite “shall connect Paris with the poles : quarries still show the marks of the " let this girdle - be the standard of chisel that cut out those wonderful measure, and let men be sent out to obelisks from them. Here he found, or “ ascertain its amount.” A magnificent somebody found for him, a telescope order, truly! Yet it does seem easy ready to his hand—the earliest telescope enough to count by thirties and by tens on record. It was a reflecting telescope, -to make the month thirty days, and like Herschel's, polished by nature's the week ten; but to measure the cirown machinery. The mirror was the cumference of the earth, this is a work, surface of standing water, and the tube a labour! It so happened, however, was one of those vertical shafts which, as that the thirty days, and the new sunin Joseph's well, have stood the wear of dials, and the unscriptural sabbaths ages, and are wonderful even in the failed to struggle into existencema land of the pyramids and the sphinxes. higher power protected France from herFar, far down in the bowels of the earth, self; whilst the measure of the merithe brighter stars were visible by day. dians—a work beset with appalling diffiThis telescope disclosed the fact, that culties-was accomplished; and the Syene is just under the northern tropic. mètre, the ten-millionth part of the And so Eratosthenes, like his great bene measured quadrant of the earth's cirfactor Alexander, conquered the world. cumference, is the national standard He did not weep because there were no throughout France to this day. more worlds to conquer; for were not The work was carried on when France the bright orbs, the allies of his first was embroiled with all Europe. The victory, like the Thebans, sure to be great men who executed it had to come an easy prey to his chariot-wheels? combat with national prejudices and But the work of Eratosthenes was done, popular superstitions in a foreign land. and they gave him as a reward a moun Privation, anxiety, and fatigue laid tain in the moon, which bears his name. some of the foremost of them low. One
To be sure, the 250,000 stadia which owed his life to the protection afforded Eratosthenes estimated as the circumfe by a Spanish prison ; another broke his rence of the earth, was a rough enough heart, on regaining his liberty, by the approximation as compared with the discovery that the observations he had precision of modern times. But it was made from his prison windows would a great work for one man,
Since then, not bear the breath of the free air.
M. Arago, in his autobiography, gives movably in the heavens, it might have an amusing, but perhaps an exaggerated, been easy, or, at least, it might have sketch of his own share in these labours. been deemed, easy, to compare his He tells us that he commenced by pacing distance with the size of the earth. to and fro, for the space of six months, But the sun wanders among the stars on the narrow platform of a rock which and rolls round the earth, and thus overlooks the Mediterranean, to watch seems to defy the efforts of the measurer. for the signal-light from the island of It was the good fortune of James Iviza. From this airy spot he was Gregory to point out a method by which transferred to the closer atmosphere of his distance may be determined, spite the castle of Belver, wounded, and a of his unsteadiness. The orbits of the prisoner. Here he had the satisfaction two planets, Mercury and Venus, lie of reading in the Spanish papers a de between the sun and the earth, so that tailed account of his own execution. those planets occasionally cross the face Judging that the announcement was of the sun-Mercury freqnently, Venus but the prelude to the event, he looked more rarely. It occurred to Gregory about for the means of escape.
From that observers at different parts of the the window of his prison he finds he earth's surface would witness a transit can leap into the sea, and he resolves across different parts of the sun-one on doing so ; conceiving, as he says, seeing it cross the centre, another observ“ that it is as well to be drowned as to ing it graze the edge. And, as the time it be hanged.” But he is not drowned. took in crossing might be readily ascerHe reaches a ship, and is conveyed to tained in either case, the places at which the coast of Africa, where he finds the it crossed would be thereby determined. Moors almost as uncivilized as the And thus, knowing the positions of the Spaniards. So he is not sorry when he two places of observation, and the coris allowed to return to his work. Once responding positions of the projection more in Spain, he is not long in dis of the planet on the sun's disk, the covering that brigandage is one of the determination of the distance of the institutions of the country. His tem sun would, by a little help from theory, porary station, on the top of a mountain be reduced to a mere matter of triangles. near Cullera, is visited, one stormy Perhaps Gregory hardly appreciated the night, by the chief bandit of the district. full value of the suggestion he was The astronomer makes him his friend, making. At any rate, nothing followed and the work proceeds merrily under the publication of his hint for a great his protection.
number of years. At length, about the Enough. We have measured the earth, beginning of the last century, it assumed, but we are a great way from the stars in the mind of Halley, the definite and still. Our yard measure has brought practicable form which renders it now ns thousands of miles on our journey ; the corner-stone of astronomy. Halley but the stars are millions of millions of perceived that the planet Venus was miles away, and how are we to get at greatly to be preferred to Mercury for them? We shall see. Remember, then, the determination of the sun's distance that, when we had a base line of a few from the earth. His lucid statements miles, we could determine the distance and earnest exhortations aroused the of an object seen from either end, by whole astronomical world, and a transit means of angles alone. In the same of Venus was anxiously awaited. Halley way, we get at the distance of the sun, himself, indeed, when he directed ator of a planet, by the longer base-line tention to the importance of the method, of the earth itself. We get at it roughly, had no hope of living to see it tested. it must be confessed. Copernicus, He stood like Moses on the top of Tycho, even Kepler himself, had no idea Pisgah, and looked on the Promised that the sun is so far from us as he Land; but to cross the Jordan was not really is. Had the sun been fixed im his earthly lot. He had been laid with