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of resource in that case, as those of the Missouri. The question then recurs whether the equatorial, without the auxiliary of a time-keeper, is not competent to the ascertainment of longitudes at land, where a fixed meridian can always be obtained ? and whether indeed it may not everywhere at land, be a readier and preferable instrument for that purpose ? To these questions I ask your attentions; and to show the grounds on which I entertain the opinion myself, I will briefly explain the principles of the process, and the peculiarities of the instrument which give it the competence I ascribe to it. And should you concur in the opinion, I will further ask you to notice any particular circumstances claiming attention in the process, and the corrections which the observations may necessarily require. As to myself, I am an astronomer of theory only, little versed in practical observations, and the minute attentions and corrections they require. I proceed now to the explanation.
A method of finding the longitude of a place at land, without a time-keeper.
If two persons, at different points of the same hemisphere, (as Greenwich and Washington, for example,) observe the same celestial phenomenon, at the same instant of time, the difference of the times marked by their respective clocks is the difference of their longitudes, or the distance between their meridians. To catch with precision the same instant of time for these simultaneous observations, the moon's motion in her orbit is the best element; her change of place (about a half second of space in a second of time) is rapid enough to be ascertained by a good instrument with sufficient precision for the object. But suppose the observer at Washington, or in a desert, to be without a timekeeper; the equatorial is the instrument to be used in that case. Again, we have supposed a cotemporaneous observer at Greenwich. But his functions may be supplied by the nautical almanac, adapted to that place, and enabling us to calculate for any instant of time the meridian distances there of the heavenly bodies necessary to be observed for this purpose.
The observer at Washington, choosing the time when their position is suitable, is to adjust his equatorial to his meridian, to his latitude, and to the plane of his horizon; or if he is in a desert where neither meridian nor latitude is yet ascertained, the advantages of this noble instrument are, that it enables him to find both in the course of a few hours. Thus prepared, let him ascertain by observation the right ascension of the moon from that of a known star, or their horary distance; and, at the same instant, her horary distance from his meridian. Her right ascension at the instant thus ascertained, enter with that of the nautical almanac, and calculate, by its tables, what was her horary distance from the meridian of Greenwich at the instant she had attained that point of right ascension, or that horary distance from the same star. The addition of these meridian distances, if the moon was between the two meridians, or the subtraction of the lesser from the greater, if she was on the same side of both, is the differences of their longitudes.
This general theory admits different cases, of which the observer may avail himself, according to the particular position of the heavenly bodies at the moment of observation.
Case 1st. When the moon is on his meridian, or on that of Greenwich.
Second. When the star is on either meridian.
Third. When the moon and star are on the same side of his meridian.
Fourth. When they are on different sides.
For instantaneousness of observation, the equatorial has great advantage over the circle or sextant; for being truly placed in the meridian beforehand, the telescope may be directed sufficiently in advance of the moon's motion, for time to note its place on the equatorial circle, before she attains that point. Then observe, until her limb touches the cross-hairs; and in that instant direct the telescope to the star; that completes the observation, and the place of the star may be read at leisure. The apparatus for correcting the effects of refraction and parallax, which is fixed on the eye-tube of the telescope, saves time by renderBy the
ing the notation of altitudes unnecessary, and dispenses with the use of either a time-keeper or portable pendulum.
I have observed that, if placed in a desert where neither meridian nor latitude is yet ascertained, the equatorial enables the observer to find both in a few hours. For the latitude, adjust by the cross-levels the azimuth plane of the instrument to the horizon of the place. Bring down the equatorial plane to an exact parallelism with it, its pole then becoming vertical. nut and pinion commanding it, and by that of the semi-circle of declination, direct the telescope to the sun. Follow its path with the telescope by the combined use of these two pinions, and when it has attained its greatest altitude, calculate the latitude as when taken by a sextant.
For finding the meridian, set the azimuth circle to the horizon, elevate the equatorial circle to the complement of the latitude, and fix it by the clamp and tightening screw of the two brass segments of arches below. By the declination semicircle set the telescope to the sun's declination of the moment. Turn the instrument towards the meridian by guess, and by the combined movement of the equatorial and azimuth circles direct the telescope to the sun, then by the pinion of the equatorial alone, follow the path of the sun with the telescope. If it swerves from that path, turn the azimuth circle until it shall follow the sun accurately. A distant stake or tree should mark the meridian, to guard against its loss by any accidental jostle of the instrument. The 12 o'clock line will then be in the true meridian, and the axis of the equatorialacircle will be parallel with that of the earth. The instrument is then in its true position for the observations of the night. To the competence and the advantages of this method, I will only add that these instruments are high-priced. Mine cost thirty-five guineas in Ramsden's shop, a little before the Revolution. I will lengthen my letter, already too long, only by assurances of my great esteem and respect.
MONTICELLO, December 11, 1821. DEAR SIR,—Your letter of December the 19th places me under a dilemma, which I cannot solve but by an exposition of the naked truth. I would have wished this rather to have remained as hitherto, without inquiry; but your inquiries have a right to be answered. I will do it as exactly as the great lapse of time and a waning memory will enable me. I may misremember indifferent circumstances, but can be right in substance.
At the time when the republicans of our country were so much alarmed at the proceedings of the federal ascendency in Congress, in the executive and the judiciary departments, it became a matter of serious consideration how head could be made against their enterprises on the constitution. The leading republicans in Congress found themselves of no use there, brow-bcaten, as they were, by a bold and overwhelming majority. They concluded to retire from that field, take a stand in the State legislatures, and endeavor there to arrest their progress. The alien and sedition laws furnished the particular occasion. The sympathy between Virginia and Kentucky was more cordial, and more intimately confidential, than between any other two States of republican policy. Mr. Madison came into the Virginia legislature. I was then in the Vice-Presidency, and could not leave my station. But your father, Colonel W. C. Nicholas, and myself happening to be together, the engaging the co-operation of Kentucky in an energetic protestation against the constitutionality of those laws, became a subject of consultation. Those gentlemen pressed me strongly to sketch resolutions for that purpose, your father undertaking to introduce them to that legislature, with a solemn assurance, which I strictly required, that it should not be known from what quarter they came.
I drew and delivered them to him, and in keeping their origin secret, he fulfilled his pledge of honor. Some years after this, Colonel Nicholas asked me if I would have any objection to its being known that I had drawn them. I pointedly enjoined that it should not. Whether he had
unguardedly intimated it before to any one, I know not; but I afterwards observed in the papers repealed imputations of them to me; on which, as has been my practice on all occasions of imputation, I have observed entire silence. The question, indeed, has never before been put to me, nor should I answer it to any other than yourself; seeing no good end to be proposed by it, and the desire of tranquillity inducing with me a wish to be withdrawn from public notice. Your father's zeal and talents were too well known, to derive any additional distinction from the penning these resolutions. That circumstance, surely, was of far less merit than the proposing and carrying them through the legislature of his State. The only fact in this statement, on which my memory is not distinct, is the time and occasion of the consultation with your father and Colonel Nicholas. It took place here I know; but whether any other person was present, or communicated with, is my doubt. I think Mr. Madison was either with us, or consulted, but my memory is uncertain as to minute details.
I fear, dear Sir, we are now in such another crisis, with this difference only, that the judiciary branch is alone and single handed in the present assaults on the constitution. But its assaults are more sure and deadly, as from an agent seemingly passive and unassuming. May you and your cotemporaries meet them with the same determination and effect, as your father and his did the alien and sedition laws, and preserve inviolate a constitution, which, cherished in all its chastity and purity, will prove in the end a blessing to all the nations of the earth. With these prayers, accept those for your own happiness and prosperity.
TO MESSRS. GEORGE W. SUMMERS AND JOHN B. GARLAND.
MONTICELLO, February 27, 1822. GENTLEMEN,—I have received your favor of the 18th, and am duly sensible of the honor done my name by its association with the institution formed in your college for improvement in the art