Imagens das páginas
PDF
ePub

read this page, who does not know that he | tal shears, or some youthful affection (in thinks more humbly of himself now, than the case of sentimental people) came to he did ten years since. And ten years nothing; and it was like cutting a tree hence, if we live, we shall think of our-over, not far above the roots, when a man selves more humbly still.

Yes we have all been severely pruned, in many ways. Perhaps our sprays and blossoms have been shred away by a knife so unsparing, that we are cut very much into the form of a pollarded tree. Perhaps we have been pruned too much, and the spring and the nonsense taken out of us only too effectually. Certain awkward knots are left in the wood, where some cherished hope was snipped off by the fa

was made to feel that his entire aim in life was no better than a dismal failure. But it was all for the best; and defeat, bravely borne, is the noblest of victories. What an overbearing, insolent person you would have been, if you had always got your own way; if your boyish fancies had come true! What an odd stick you would have become, had you been one of the Unpruned Trees! A. K. H. B.

From Chambers's Journal.

THERMOMETERS.

AN ordinary thermometer consists, as every body knows, of a glass tube fixed to a scale. This tube contains a fine bore, and has a bulb blown at one extremity. Some liquid, generally mercury or alcohol, is introduced into the tube, the air is driven out, and the tube is sealed. The quantity of fluid, say mercury, admitted into the tube is so regulated that at common temperatures the bulb and a portion of the bore are filled. The remainder of the bore, which is empty, affords space for the mercury to rise. This arrangement renders very perceptible the alterations in the volume of the mercury due to changes of temperature, a very slight increase or diminution of volume causing the mercury to rise or to fall appreciably in the fine bore. After sealing, the scale has to be adjusted to the tube, and the instrument is complete.

Thermometers of the most accurate make are called standard thermometers. In their manufacture, numerous precautions are necessary from the very outset. Even in so simple a matter as the choice of the tube of glass, much care is requisite. The bore has to be tested in order to insure that it is of uniform capacity throughout. It is found that tubes, as they come from the glass-house, contain a bore wider at one extremity than the other.

The

bore is, in fact, a portion of a very elongated cone. In a hundred-weight of tubes not more than half-a-dozen or so can be picked out in which the bore is perfectly true. The bore is tested in a very ingenious, though simple manner. A bulb is blown, and a very small quantity of mercury is admitted into the tube, about as much as will fill an inch and a half of the bore.

By alternately cooling and heating the bulb, this delicate thread of mercury is driven from one end of the tube to the other, and during this process its length is carefully measured in all parts of the tube. Should the length of the mercury alter in various situations, it is evident that the capacity of the bore is not uniform throughout, and the tube must be rejected. In blowing the bulb, an elastic ball containing air is used. The ordinary method of blowing glass bulbs by means of the breath, is found to cause the introduction of moisture into the tube.

The size of the bulb has next to be considered. A large bulb renders the instrument slow in its indications of change, owing to the quantity of mercury that has to be acted on. On the other hand, if the bulb is too small, it will not contain sufficient mercury to register high temperatures, unless the bore is exceedingly fine.

The shape of the bulb is of importance.

in the tube after filling; and when the expulsion of air and moisture is deemed complete, and while the mercury fills the tube, the artist dexterously removes it from the source of heat, and at the same moment closes it with the flame of a blowpipe. It sometimes happens that, in spite of every care, a little air still remains in the tube. Its presence is detected by inverting the tube, when, if the mercury falls to the extremity (or nearly so) of the bore, some air is present, which, of course, must be removed.

Spherical bulbs are best adapted to resist the varying pressure of the atmosphere; while cylindrical bulbs expose larger surfaces of mercury, and are therefore preferred for more delicate instruments. Various plans have been suggested in order to obtain thermometers of extreme sensitiveness for delicate experiments. Some have been made with very small thin bulbs, to contain a very small quantity of mercury; but in these the indicating column is generally so fine that it can only be read by the aid of a powerful lens. Instruments have been contrived with The thermometer, after being filled, has spiral or coiled tubular bulbs; but the to be graduated. Common thermometers thickness of glass required to keep these are fixed to a scale on which the degrees in shape nullifies the effect sought to be are marked; but the graduation of standobtained-namely, instantaneous action. ards is engraved on the stem itself, in Messrs. Negretti & Zambra, the well- order to insure the greatest possible acknown meteorological instrument-makers, curacy. The first steps in graduating are have recently succeeded in constructing a to ascertain the exact freezing-point and thermometer which combines sensitive- the exact boiling point, and to mark on ness and quickness of action, and which presents a good visible column. The bulb of this thermometer is of a gridiron form. The reservoir is made of glass, so thin that it can not be blown; it can only be formed by means of a spirit-lamp, yet its shape gives it such rigidity that its indications are not affected by altering its position or by standing it on its bulb. The reservoirs of the most delicate of these instruments contain about nine inches of excessively thin cylindrical glass, the outer diameter of which is not more than the twentieth of an inch, and, owing to the large surface thus presented to the air, the indications are positively instantaneous. This form of thermometer was constructed expressly to meet the require ments of scientific balloon ascents, to enable the observer to take. thermometric readings at precise elevations. It was contemplated to procure a metallic thermometer, but, on the production of this perfect instrument, the idea was abandoned.

The shape and size of the bulb having been determined, the workman next proceeds to fill the tube. This is effected by heating the bulb while the open end of the tube is embedded in mercury. Upon allowing the bulb to cool, the atmospheric pressure drives some mercury into the tube. The process is continued until sufficient mercury has entered. The mercury used in filling should be quite pure, and should have been freed from moisture and air by recent boiling. It is again boiled

the tube the height of the mercury at these points. The freezing-point can be determined with comparative ease. Melting ice has always the same temperature in all places and under all circumstances, provided only that the water from which the ice is congealed is pure. The bulb and the lower portion of the tube are immersed in melting ice; the mercury descends; the point where it remains stationary is the freezing-point, and is marked on the tube.

The determination of the boiling-point is more difficult. The boiling-point varies with the pressure of the atmosphere. The normal boiling temperature of water is fixed at a barometric pressure of 29.922 inches of mercury having the temperature of melting ice, in the latitude of 45°, and at the level of the sea. Of course, these conditions rarely, if ever, coëxist; and consequently the boiling-point has to be corrected for errors, and reduced for latitude. Tables of vapor tension, as they are called, computed from accurate experiments, are used for this purpose. Regnault's tables, the most recent, are considered the best.

An approximate boiling-point is first obtained by actual experiment. A copper boiler is used, which has at its top an open cylinder two or three inches in diameter, and of sufficient length to allow a thermometer to be introduced into it without touching the water in the boiler. The cylinder is surrounded by a second one, fixed to the top of the boiler, but not en

tering it, the two being about an inch | respects. The meteorological observer is apart. The outer cylinder is intended to seldom troubled with negative signs, the protect the inner one from contact with divisions of the scale are numerous, and the cold external air. The thermometer tenths of degrees give all the minuteness to be graduated is placed in the inner usually requisite. cylinder, and held there by a thong of india-rubber. As the vapor of the boiling water rises from the boiler into the cylinder, it envelops the thermometer, and causes the mercury to ascend. As the mercury rises, the tube is gradually lowered, so as to keep the top of the mercury just visible above the cylinder. When the mercury becomes stationary, the position of the top of the column is marked on the tube; and the boiling-point, subject to corrections for errors, is obtained.

In 1742, Celsius, a Swede, proposed zero for the freezing-point, and 100 deg. for the boiling-point, all temperatures below freezing being distinguished by the negative sign (-). This scale is known as the Centigrade. It is in use in France, Sweden, and in the south of Europe; it has the advantage of decimal notation, with the disadvantage of the negative sign.

Reaumur's scale is in use in Spain, Switzerland, and Germany. It differs from the Centigrade in this, that the freezing and boiling points are separated by 80 deg. instead of 100 deg.

The freezing and boiling points being determined, the scale is applied by dividing the length between the two points into a certain number of equal degrees. It would not be difficult to construct a This operation is performed by a machine scale which should combine all the advancalled a dividing-engine, which engraves tages of Fahrenheit's and of the Centidegrees of any required width with ex-grade. Freezing-point should be fixed at treme accuracy.

100 deg.; and boiling-point should be fixed at as many hundred divisions or degrees above 100 degrees as might be agreed on by practical men as most convenient. The advantages of decimal notation would thus remain as in the Centigrade scale, and the minus sign would be got rid of.

The scale used in the United Kingdom, in the British colonies, and in North America, is that known as Fahrenheit's. Fahrenheit was a philosophical instrumentmaker of Amsterdam. About the year 1724 he invented the scale with which his name is associated. The freezingpoint of his scale is 32 deg., the boiling- And now, having applied the scale, and point 212 deg., and the intermediate space having exercised every precaution, can we is composed of 180 deg. This peculiar congratulate ourselves on possessing a division was thus derived. The lowest perfect instrument? Disheartening as it cold observed in Iceland was the zero of may appear, the standard instrument of Fahrenheit. When the thermometer to-day may not be accurate to morrow. stood at zero, it was calculated to contain It is more than probable that the freezinga volume of mercury represented by the point will become displaced. This curious figures 11,124. When plunged into melt-phenomenon has never been satisfactorily ing snow, the mercury expanded to a explained. Messrs. Negretti & Zambra, volume represented by 11,156; hence the in their treatise On Meteorological Inintermediate space was divided into thir-struments (a work which abounds with ty-two equal portions or degrees, and information of a most interesting nature), thirty-two was taken as the freezing-point of water. Similarly, at the boiling-point, the quicksilver expanded to 11,336. Fahrenheit's scale is convenient in some

* Mr. Balfour Stewart has lately concluded a series of experiments at the Kew Observatory, by which he has accurately determined the freezing-point of mercury. The experiments, conducted with great care, have shown that the freezing-point of mercury, like that of water, is constant, and that it denotes a temperature of 37.93 F. The freezingpoint of mercury will now be used as a third point in graduating thermometers which are intended to register extreme temperatures.

say, in reference to displacement of the freezing-point, that "either the prolonged effect of the atmospheric pressure upon the thin glass of the bulbs of thermometers, or the gradual restoration of the equilibrium of the particles of the glass after having been greatly disturbed by the operation of boiling the mercury, seems to be the cause of the freezing-points of standard thermometers reading from a few tenths to a degree higher in the course of some years." To obviate this small error, it is the practice of the makers in question "to place the tubes aside for about six

months before fixing the freezing-point, in | order to give time for the glass to regain its former state of aggregation. The making of accurate thermometers is a task attended with many difficulties, the principal one being the liability of the zero or freezing-point varying constantly; so much so that a thermometer that is perfectly correct to-day, if immersed in boiling water, will be no longer accurate; at least it will take some time before it

again settles into its normal state. Then, again, if a thermometer is recently blown, filled, and graduated immediately, or at least before some months have elapsed, though every care may have been taken with the production of the instrument, it will require some correction; so that the instrument, however carefully made, should from time to time be plunged into finely pounded ice, in order to verify the freezing-point."

From Fraser's Magazine.

THE

TRANSCENDENTALISTS

[FAMILIAR as our readers are with the characters so racily sketched in this paper, we are sure it will be read with interest, coming from an English source, and revealing so much of the inner life of the remarkable circle which it describes. The personal friendship and sympathy of the writer give a rosy hue to the coloring; but the picture is not without its sober and instructive aspects.-Ed. ECLECTIC.]

Ir is now nearly thirty years since Ralph Waldo Emerson, having already startled the generation of young Americans from the drowsiness which they had inherited, returned from his communion with Carlyle, Coleridge, and Wordsworth, and came to his ancestral home at Concord, Massachusetts, to be the Arthur of an intellectual Round Table. The little village of Concord is about twenty miles from Boston, just too far to be an inviting place of residence to those having business with the city. It had exactly the same number of inhabitants, according to the census of 1860, that it had in 1850-about 1200. It is known among the manufacturing towns around as Sleepy Hollow. Its visitors for fifty years had been only some young patriots who came occasionally to stand on the spot where the first physical resistance was made to the soldiers of George III. by his revolutionary colonies

[blocks in formation]

"By the rude bridge that arched the flood, Their flag to April's breeze unfurled, Where once the embattled farmers stood, And fired the shot heard round the world."

But within these thirty years there have been more pilgrims to Concord than were ever attracted by the little granite shaft, and the submerged buttresses of the old bridge, which indicate the sacred spot. For in that time the seemingly sleepy little village has been the arena of a nobler revolution-that against creeds and forms whose time had come to pass away, but which still aspired to grasp and wield in their skeleton hands the scepter of the New World.

Emerson stood not only by gifts but by hereditary right the representative of whatever new unfoldings of thought might be possible under the new conditions of American life. He was the eighth in regular succession of a family line of clergymen; a most important fact in a country where the clergyman was at once the scholar and authentic spiritual guide in every community, and also a paramount power behind every magistrate; and it is well known that the Puritans did not fail to appreciate the sweets of power when they became the rulers instead of the ruled. But it is more interesting to know that these eight ministers of the family had each represented the most advanced phase of what is called "New England

Theology," in his time. The earliest an- | lar day for celebrating the Lord's Supper cestors had of course preached extreme returned, he announced to his congregaCalvinism; but no ray of liberalism that tion that he must decline to administer it. mitigated that shadow was without an He gave as his reason, that he thought Emerson standing for it. When the time the Quakers right in thinking that the of Arminianism came, Emerson's grand- Lord's Supper was an inward communion, father was in the van of its defenders, and which was only sensualized by the prehis father was one of the earliest to avow sentation of outward symbols. This Unitarianism. Ralph Waldo certainly wrought such an agitation amongst his proved himself to be, if I may be allowed fellow-ministers, that he resigned his pulthe phrase, "a chip of the old block," pit. About this time also his spirits were when he took Unitarianism, in the plain- much depressed by the loss of his wife, a tive language of an old Boston clergyman, beautiful and superior woman, whom he and carried it God knows where. Emer- married in September, 1830, and lost in son thus inherited the accumulated cul- less than five months thereafter. He then ture and heresies of two hundred years, visited Europe, where he had important inand is reverently regarded by his disciples terviews with Landor, Coleridge, Wordsas the consummate flower which the stur- worth, and more particularly with Thomas dy root and thorny stem of Puritanism Carlyle, whose genius he was perhaps one existed to produce. of the first to recognize. He traveled far, and by a private carriage, to find Craigenputtock, amid its "desolate heathery hills, where the lonely scholar nourished his mighty heart." Many will remember his account of this visit. "We went out," he says, "to walk over long hills, and looked at Criffel, then without his cap, and down into Wordsworth's country. There we sat down and talked of the immortality of the soul. It was not Carlyle's fault that we talked on that topic, for he had the natural disinclination of every nimble spirit to bruise itself against walls, and did not like to place himself where no step can be taken. But he was honest and true, and cognizant of the subtle links that bind ages together, and saw how every event affects all the future. "Christ died on the tree: that built Dunscone kirk yonder: that brought you and me together. Time has only a relative exist ence."

[ocr errors]

It is a part of the Boston creed that one who is born in that city does not need to be born again. Destiny gave this advantage to Emerson, May 25th, 1803. He had the usual advantages, also, of a boy of good family, brought up in a city where, as I think, more careful attention is paid to the real education of children than in any other part of the world. So early as the age of fourteen he entered Harvard University, at Cambridge, where he was graduated in 1821. He had the much sought distinction of being the Class-Poet on class-day. He did not take a very high rank in his class, though, during his college course, he had twice received a Bowdoin prize for dissertations, and once a Boylston prize for declamation. Amongst his companions he was distinguished for general literary attainments. After graduation, Emerson studied in the Divinity College at Cambridge, and at the same time taught school; this extra labor was undertaken for the purpose of educating, at Harvard, his younger brother Charles, who was by many at that time regarded as intellectually superior to Ralph Waldo. This young man died soon after graduation, leaving behind him a few remarkable manuscripts, which were published in the Dial, as "Notes from the Journal of a Scholar." In 1826, Emerson was "approbated" by the Middlesex Association of Ministers; but, his health failing, he spent the winter in Florida and South Carolina. In 1829 he was ordained pastor of a church of importance in Boston. He had been in this position a year or two when, as the regu

On his return from Europe in the winter of 1833, Emerson began his career as a lecturer, and really created the Lyceum system of America. The successive subjects upon which he lectured during the next few years indicate the direction of his studies: "Water;""Italy" (2); "The Relation of Man to the Globe" (3); "Michel Angelo;" "Milton;" "Luther;" "George Fox; ""Edmund Burke."

In the year 1835 Mr. Emerson was a second time married, and went to reside in Concord. In the same year he began to be known as one who was giving new views to the people. Large and anxious crowds attended his lectures on "The Times," on "The American Scholar," on

« AnteriorContinuar »