Kitabı oku: «The Writings of Thomas Jefferson, Vol. 6 (of 9)», sayfa 45

TO MR. GEORGE FLEMING

Monticello, December 29, 1815.

Sir,—At the date of your favor of October 30th, I had just left home on a journey to a distant possession of mine, from which I am but recently returned, and I wish that the matter of my answer could compensate for its delay. But, Sir, it happens that of all the machines which have been employed to aid human labor, I have made myself the least acquainted with (that which is certainly the most powerful of all) the steam engine. In its original and simple form indeed, as first constructed by Newcomen and Savary, it had been a subject of my early studies; but once possessed of the principle, I ceased to follow up the numerous modifications of the machinery for employing it, of which I do not know whether England or our own country has produced the greatest number. Hence, I am entirely incompetent to form a judgment of the comparative merit of yours with those preceding it; and the cession of my library to Congress has left me without any examples to turn to. I see, indeed, in yours, the valuable properties of simplicity, cheapness and accommodation to the small and more numerous calls of life, and the calculations of its power appear sound and correct. Yet experience and frequent disappointment have taught me not to be over-confident in theories or calculations, until actual trial of the whole combination has stamped it with approbation. Should this sanction be added, the importance of your construction will be enhanced by the consideration that a smaller agent, applicable to our daily concerns, is infinitely more valuable than the greatest which can be used only for great objects. For these interest the few alone, the former the many. I once had an idea that it might perhaps be possible to economize the steam of a common pot, kept boiling on the kitchen fire until its accumulation should be sufficient to give a stroke, and although the strokes might not be rapid, there would be enough of them in the day to raise from an adjacent well the water necessary for daily use; to wash the linen, knead the bread, beat the homony, churn the butter, turn the spit, and do all other household offices which require only a regular mechanical motion. The unproductive hands now necessarily employed in these, might then increase the produce of our fields. I proposed it to Mr. Rumsey, one of our greatest mechanics, who believed in its possibility, and promised to turn his mind to it. But his death soon after disappointed this hope. Of how much more value would this be to ordinary life than Watts & Bolton's thirty pair of mill-stones to be turned by one engine, of which I saw seven pair in actual operation. It is an interesting part of your question, how much fuel would be requisite for your machine?

Your letter being evidence of your attention to mechanical things, and to their application to matters of daily interest, I will mention a trifle in this way, which yet is not without value. I presume, like the rest of us in the country, you are in the habit of household manufacture, and that you will not, like too many, abandon it on the return of peace, to enrich our late enemy, and to nourish foreign agents in our bosom, whose baneful influence and intrigues cost us so much embarrassment and dissension. The shirting for our laborers has been an object of some difficulty. Flax is injurious to our lands, and of so scanty produce that I have never attempted it. Hemp, on the other hand, is abundantly productive, and will grow forever on the same spot. But the breaking and beating it, which has been always done by hand, is so slow, so laborious, and so much complained of by our laborers, that I had given it up and purchased and manufactured cotton for their shirting. The advanced price of this, however, now makes it a serious item of expense; and in the meantime, a method of removing the difficulty of preparing hemp occurred to me, so simple and so cheap, that I return to its culture and manufacture. To a person having a threshing machine, the addition of a hemp-break will not cost more than twelve or fifteen dollars. You know that the first mover in that machine is a horizontal horse-wheel with cogs on its upper face. On these is placed a wallower and shaft, which give motion to the threshing apparatus. On the opposite side of this same wheel I place another wallower and shaft, through which, and near its outer end, I pass a cross-arm of sufficient strength, projecting on each side fifteen inches in this form: nearly under the cross-arm is placed a very strong hemp-break, much stronger and heavier than those for the hand. Its head block particularly is massive, and four feet high, and near its upper end in front, is fixed a strong pin (which we may call its horn), by this the cross-arm lifts and lets fall the break twice in every revolution of the wallower. A man feeds the break with hemp stalks, and a little person holds under the head block a large twist of the hemp which has been broken, resembling a twist of tobacco but larger, where it is more perfectly beaten than I have ever seen done by hand. If the horse-wheel has one hundred and forty-four cogs, the wallower eleven rounds, and the horse goes three times round in a minute, it will give about eighty strokes in a minute. I had fixed a break to be moved by the gate of my saw-mill, which broke and beat at the rate of two hundred pounds a day. But the inconveniences of interrupting that, induced me to try the power of a horse, and I have found it to answer perfectly. The power being less, so also probably will be the effect, of which I cannot make a fair trial until I commence on my new crop. I expect that a single horse will do the breaking and beating of ten men. Something of this kind has been so long wanted by the cultivators of hemp, that as soon as I can speak of its effect with certainty, I shall probably describe it anonymously in the public papers, in order to forestall the prevention of its use by some interloping patentee. I shall be happy to learn that an actual experiment of your steam engine fulfils the expectations we form of it, and I pray you to accept the assurances of my esteem and respect.

TO M. DUPONT DE NEMOURS

Monticello, December 31, 1815.

Nothing, my very dear and ancient friend, could have equalled the mortification I felt on my arrival at home, and receipt of the information that I had lost the happiness of your visit. The season had so far advanced, and the weather become so severe, that together with the information given me by Mr. Correa, so early as September, that your friends even then were dissuading the journey, I had set it down as certain it would be postponed to a milder season of the ensuing year. I had yielded, therefore, with the less reluctance to a detention in Bedford by a slower progress of my workmen than had been counted on. I have never more desired anything than a full and free conversation with you. I have not understood the transactions in France during the years '14 and '15. From the newspapers we cannot even conjecture the secret and real history; and I had looked for it to your visit. A pamphlet (Le Conciliateur) received from M. Jullien, had given me some idea of the obliquities and imbecilities of the Bourbons, during their first restoration. Some manœuvres of both parties I had learnt from Lafayette, and more recently from Gallatin. But the note you referred me to at page 360 of your letter to Say, has possessed me more intimately of the views, the conduct and consequences of the last apparition of Napoleon. Still much is wanting. I wish to know what were the intrigues which brought him back, and what those which finally crushed him? What parts were acted by A, B, C, D., &c, some of whom I know, and some I do not? How did the body of the nation stand affectioned, comparatively, between the fool and the tyrant? &c., &c., &c. From the account my family gives me of your sound health, and of the vivacity and vigor of your mind, I will still hope we shall meet again, and that the fine temperature of our early summer, to wit, of May and June, may suggest to you the salutary effects of exercise, and change of air and scene. En attendant, we will turn to other subjects.

That your opinion of the hostile intentions of Great Britain towards us is sound, I am satisfied, from her movements north and south of us, as well as from her temper. She feels the gloriole of her late golden achievements tarnished by our successes against her by sea and land; and will not be contented until she has wiped it off by triumphs over us also. I rely, however, on the volcanic state of Europe to present other objects for her arms and her apprehensions; and am not without hope we shall be permitted to proceed peaceably in making children, and maturing and moulding our strength and resources. It is impossible that France should rest under her present oppressions and humiliations. She will rise in that gigantic strength which cannot be annihilated, and will fatten her fields with the blood of her enemies. I only wish she may exercise patience and forbearance until divisions among them may give her a choice of sides. To the overwhelming power of England I see but two chances of limit. The first is her bankruptcy, which will deprive her of the golden instrument of all her successes. The other in that ascendency which nature destines for us by immutable laws. But to hasten this last consummation, we too must exercise patience and forbearance. For twenty years to come we should consider peace as the summum bonum of our country. At the end of that period we shall be twenty millions in number, and forty in energy, when encountering the starved and rickety paupers and dwarfs of English workshops. By that time I hope your grandson will have become one of our High-admirals, and bear distinguished part in retorting the wrongs of both his countries on the most implacable and cruel of their enemies. In this hope, and because I love you, and all who are dear to you, I wrote to the President in the instant of reading your letter of the 7th, on the subject of his adoption into our navy. I did it because I was gratified in doing it, while I knew it was unnecessary. The sincere respect and high estimation in which the President holds you, is such that there is no gratification, within the regular exercise of his functions, which he would withhold from you. Be assured then that, if within that compass, this business is safe.

Were you any other than whom you are, I should shrink from the task you have proposed to me, of undertaking to judge of the merit of your own translation of the excellent letter on education. After having done all which good sense and eloquence could do on the original, you must not ambition the double need of English eloquence also. Did you ever know an instance of one who could write in a foreign language with the elegance of a native? Cicero wrote Commentaries of his own Consulship in Greek; they perished unknown, while his native compositions have immortalized him with themselves. No, my dear friend; you must not risk the success of your letter on foreignisms of style which may weaken its effect. Some native pen must give it to our countrymen in a native dress, faithful to its original. You will find such with the aid of our friend Correa, who knows everybody, and will readily think of some one who has time and talent for this work. I have neither. Till noon I am daily engaged in a correspondence much too extensive and laborious for my age. From noon to dinner health, habit, and business, require me to be on horseback; and render the society of my family and friends a necessary relaxation for the rest of the day. These occupations scarcely leave time for the papers of the day; and to renounce entirely the sciences and belles-lettres is impossible. Had not Mr. Gilmer just taken his place in the ranks of the bar, I think we could have engaged him in this work. But I am persuaded that Mr. Correa's intimacy with the persons of promise in our country, will leave you without difficulty in laying this work of instruction open to our citizens at large.

I have not yet had time to read your Equinoctial republics, nor the letter of Say; because I am still engrossed by the letters which had accumulated during my absence. The latter I accept with thankfulness, and will speedily read and return the former. God bless you, and maintain you in strength of body, and mind, until your own wishes shall be to resign both.

TO CAPT. A. PARTRIDGE

Monticello, January 2d, 1816.

Sir,—I am but recently returned from my journey to the neighborhood of the Peaks of Otter, and find here your favors of November 23d and December 9th. I have therefore to thank you for your meteorological table and the corrections of Colonel Williams' altitudes of the mountains of Virginia, which I had not before seen; but especially for the very able extract on Barometrical measures. The precision of the calculations, and soundness of the principles on which they are founded, furnish, I am satisfied, a great approximation towards truth, and raise that method of estimating heights to a considerable degree of rivalship with the trigonometrical. The last is not without some sources of inaccuracy, as you have truly stated. The admeasurement of the base is liable to errors which can be rendered insensible only by such degrees of care as have been exhibited by the mathematicians who have been employed in measuring degrees on the surface of the earth. The measure of the angles by the wonderful perfection to which the graduation of instruments has been brought by a Bird, a Ramsden, a Troughton, removes nearly all distrust from that operation; and we may add that the effect of refraction, rarely worth notice in short distances, admits of correction by well-established laws; these sources of error once reduced to be insensible, their geometrical employment is certainty itself. No two men can differ on a principle of trigonometry. Not so as to the theories of Barometrical mensuration. On these have been great differences of opinion, and among characters of just celebrity.

Dr. Halley reckoned one-tenth inch of Mercury equal to 90 feet altitude of the atmosphere. Derham thought it equal to something less than 90 feet. Cassini's tables to 24° of the Barometer allowed 676 toises of altitudes.

Nettleton's tables applied to a difference of .5975 of mercury, in a particular instance gave 512.17 feet of altitude, and Bonguor's and De Luc's rules, to the same difference gave 579.5 feet. Sir Isaac Newton had established that at heights in arithmetrical progression the ratio of rarity in the air would be geometrical, and this being the character of the natural numbers and their Logarithms, Bonguor adopted the ratio in his mensuration of the mountains of South America, and stating in French lignes the height of the mercury of different stations, took their Logarithms to five places only, including the index, and considered the resulting difference as expressing that of the altitudes in French toises. He then applied corrections required by the effect of the temperature of the moment on the air and mercury. His process, on the whole, agrees very exactly with that established in your excellent extract. In 1776 I observed the height of the mercury at the base and summit of the mountain I live on, and by Nettleton's tables, estimated the height at 512.17 feet, and called it about 500 feet in the Notes on Virginia. But calculating it since on the same observations, according to Bonguor's method with De Luc's improvements, the result was 579.5 feet; and lately I measured the same height trigonometrically, with the aid of a base of 1,175 feet in a vertical plane with the summit, and at the distance of about 1,500 yards from the axis of the mountain, and made it 599.35 feet. I consider this as testing the advance of the barometrical process towards truth by the adoption of the Logarithmic ratio of heights and densities; and continued observations and experiments will continue to advance it still more. But the first character of a common measure of things being that of invariability, I can never suppose that a substance so heterogeneous and variable as the atmospheric fluid, changing daily and hourly its weight and dimensions to the amount, sometimes, of one-tenth of the whole, can be applied as a standard of measure to anything, with as much mathematical exactness, as a trigonometrical process. It is still, however, a resource of great value for these purposes, because its use is so easy, in comparison with the other, and especially where the grounds are unfavorable for a base; and its results are so near the truth as to answer all the common purposes of information. Indeed, I should in all cases prefer the use of both, to warn us against gross error, and to put us, when that is suspected, on a repetition of our process. When lately measuring trigonometrically the height of the Peaks of Otter (as my letter of October 12th informed you I was about to do), I very much wished for a barometer, to try the height of that also. But it was too far and hazardous to carry my own, and there was not one in that neighborhood. On the subject of that admeasurement, I must premise that my object was only to gratify a common curiosity as to the height of those mountains, which we deem our highest, and to furnish an à peu près, sufficient to satisfy us in a comparison of them with the other mountains of our own, or of other countries. I therefore neither provided such instruments, nor aimed at such extraordinary accuracy in the measures of my base, as abler operators would have employed in the more important object of measuring a degree, or of ascertaining the relative position of different places for astronomical or geographical purposes. My instrument was a theodolite by Ramsden, whose horizontal and vertical circles were of 3½ inches radius, its graduation subdivided by noniuses to one-third, admitting however by its intervals, a further subdivision by the eye to a single minute, with two telescopes, the one fixed, the other movable, and a Gunter's chain of four poles, accurately adjusted in its length, and carefully attended on its application to the base line. The Sharp, or southern peak, was first measured by a base of 2806.32 feet in the vertical plane of the axis of the mountain. A base then nearly parallel with the two mountains of 6,589 feet was measured, and observations taken at each end, of the altitudes and horizontal angles of each apex, and such other auxiliary observations made as to the stations, inclination of the base, &c., as a good degree of correctness in the result would require. The ground of our bases was favorable, being an open plain of close grazed meadow on both sides of the Otter river, declining so uniformly with the descent of the river as to give no other trouble than an observation of its angle of inclination, in order to reduce the base to the plane of the horizon. From the summit of the Sharp peak I took also the angle of altitude of the flat or northern one above it, my other observations sufficing to give their distance from one another. The result was,

Their rhumb N. 33° 50´ E. the distance of the stations of observation from the points in the bases of the mountains vertically under their summits was, the shortest 19002.2 feet, the longest 24523.3 feet. These mountains are computed to be visible to fifteen counties of the State, without the advantage of counter-elevations, and to several more with that advantage. I must add that I have gone over my calculations but once, and nothing is more possible than the mistake of a figure, now and then, in calculating so many triangles, which may occasion some variation in the result. I mean, therefore, when I have leisure, to go again over the whole. The ridge of mountains of which Monticello is one, is generally low; there is one in it, however, called Peter's mountain, considerably higher than the general ridge. This being within a dozen miles of me, north-eastwardly, I think in the spring of the year to measure it by both processes, which may serve as another trial of the Logarithmic theory. Should I do this you shall know the result. In the meantime accept assurances of my great respect and esteem.