« ZurückWeiter »
alienum, lente acceptum exuit); quare augescit magnitudo divergentiæ, quæ fit abs igne aereo, non mutata magnitudine absoluta ignis aerei, sed mutata solum magnitudine ipsius comparativa, minuto nempe igne proprio; adeoque aucta proportione aerei ad proprium. Igitur quoniam quantum ignis ingeritur in catenam, tantundem subtrahitur a machina; proportio ignis aerei circa machinam ad residuum in machina eadem erit ac proportio ignis in catena redundantis ad aereum circa catenam; quamobrem aereus circa machinam discessiones faciet non æque veloces solum, sed et æque magnas, ac eæ sunt, quas facit ignis proprius in catena.
28. Itaque, ut omnia demum paucis complectar, quæ pertinere videntur ad motus electricos universe omnes explicandos (suspensiones enim, adhæsiones, vibrationes, infinitosque alios compositiores quasi ludos electricos, tu ipse probe videre visus es discessionibus omnes, atque accessionibus contineri), hæc denique est summa hypothesis meæ. "Accessiones corporum inæqualiter electricorum efficiuntur ab igne electrico a corpore altero, in quo copiosior est, effluente in alterum per aerem interjectum, ipsumque disjiciente. Discessiones autem vel igne proprio corporum efficiuntur se expandente contra aereum, vel aereo se expandente valentius contra proprium;" quæ tamen expansio ignis alterius alterum superantis sine mixtione mutua alterius cum altero videtur contingere. Aer enim ignem continet suum quantumcunque, ne discedat; arcet proprium deferentium corporum ignem, ne adhærescat sibi.
29. Hanc, inquam, hypothesim offero tibi, vir præclarissime, quo tu eam facias meliorem. Si tanti interea ipsam ducas, ut Regiæ isti scientiarum Societati exhibenda videatur, res ex meo obtinget desiderio, qui quando ornamentum ipsi adferre nullum possum, diligentiam saltem nolim desiderari meam. Tu vero cura, ut valeas. Servari enim te decet quam diutissime utilissime, scientiæ perficiendæ amplificandæque, quam certissimam instituisti.
Dat. Taurini, 24 Decembris, 1757.
Remarks on the preceding Paper, by Dr. Franklin.
For the better understanding this paper, it is necessary to know, that Father Beccaria uses a large chain, suspended by silk lines, for the purpose of a prime conductor; and that his machine for turning the glass globe is so contrived, as that he can, on occasion, readily isolate it (that is, place it on glass or wax), together with the person that works it. When the communication is thus cut off between the earth and the chain, and also between the earth
and the machine, he observes, that, the globe being turned, both the chain and the machine show signs of electricity; and, as these signs, when examined, appear to be different in the chain and in the machine, and the globe having, as he supposes, drawn from the machine part of its natural or common quantity of electricity, and given it to the chain, he calls the electricity appearing in the chain, electricity by excess; and the electricity appearing in the machine, electricity by defect; which answer to our terms of positive and negative electricity, or electricity plus and minus. And thus his expressions, electrifying by the chain, and electrifying by the machine, are to be understood, electrifying positively, and electrifying negatively.
LETTER FROM PROFESSOR THORBERN BERGMAN, OF UPSAL, TO BENJAMIN WILSON.*
Remarks on One of Franklin's Experiments in Electricity. READ AT THE ROYAL SOCIETY, NOVEMBER 20тн, 1760.
DOMINUS Franklin in 28 tertiæ epistolæ miratur glaciei frustum non transmittere commotionem electricam, cum aqua idem perfecte præstet; sed feci nonnulla experimenta, quæ monstrant parvam aquæ quantitatem nec huic fini sufficere. Scilicet capiatur. tubus vitreus trium vel quatuor pedum, qualis barometris inservit ; hic aqua impleatur, et claudatur utrumque extremum subere perforato filo metallico aquam paululum intrante, uti figura adposita indicat.
Si jam duo homines in circulo explosorio constituti teneant extrema filorum metallicorum, A, A, et tentetur evacuatio, non tamen perfecta evenit, nam vix carpus et rarissime flexura cubitus hac methodo
This letter is dated at Upsal, October 17th, 1760. An extract only is here given. The remainder of the letter relates to a different subject. See the whole in the Philosophical Transactions, Vol. LI. p. 907.— EDITOR.
† See p. 209 of the present volume. — EDITOR.
concutitur, licet deinde idem vas absque ulteriori cumulatione tantum contineat electricitatis, ut more consueto evacuatum pectus valide ferire possit. Aucta tubi capacitate, magis transit, usque dum ita increverit, ut plenarium transitum permittat, nec impedit aquæ quantitas justo major, quod testantur commotiones per lacus et flumina propagatæ. Conveniunt itaque aqua et glacies in co, quod parvæ quantitates concussionem ægre tramittant.
Hinc suspicatus sum magnam glaciei quantitatem faciliorem concedere transitum, quod etiam experientia comprobavit, etsi adhuc non majus adhibui frustum quam quo commotio flexuram cubitus attigit. Præterea ex æqualibus aquæ et glaciei quantitatibus, glacies minus transmittit.
LETTER FROM M. DUBOURG TO M. DE LOR.*
Parallel between the Theories of Franklin and Nollet.
I return you the History of Electricity, which you had the goodness to lend me, with my thanks for it. Mr. Priestley's zeal for the glory of Mr. Franklin has given umbrage to the editor, who is animated with a zeal no less ardent for the memory of.the Abbé Nollet. Which would all be very well, if he did not attempt to make it a party matter between the French and English. Let us leave these national prejudices to the common people; let political ministers espouse their passions, if they think they can make them subservient to their designs; but let not philosophers be influenced by these petty local considerations. The republic of letters is one; let us have a care that we do not dismember it; it allows distinctions, but abhors a division. Nollet, Franklin, Hawksbee, Musschenbroek, pinus, Wilson, and Beccaria are all fellow-citizens, and we should regard them all with equal favor.
I will give you candidly, and I would repeat it with the same frankness before all the world, my opinion of Franklin and of
* Translated from M. Dubourg's edition of Franklin's works. M. de Lor was Professor of Experimental Philosophy in Paris. — EDITOR.
Nollet; and I will thank you to weigh my thoughts on this subject, with the same candor and impartiality.
Electricity is like an extensive and valuable field, which, after having lain fallow for a long succession of ages, has, for the last few years, been cultivated with wonderful ardor and success, but has not yielded its richest fruits. Natural philosophers of all countries have devoted themselves, in emulation of each other, to electrical researches; they have collected observations, have multiplied and varied experiments; they have constructed systems to explain facts, and to discover their causes; they have attempted to make useful applications of them; but all have not been equally skilful, nor equally successful. It is not for me to decide among them, but every one may say what he thinks. I shall use this right, while I enIdeavour not to abuse it.
And I think we should set out with this principle; of two hypotheses, the best, in my opinion, is that which, embracing all known facts, and showing their agreement and their points of difference, connects them together in such a regular order, that it is not only easy to apprehend all their relations to each other, but that we perceive, almost at the same moment, what is wanting to their completeness, and what remains to be done to fill up some blank spaces, or unite the scattered links in the great chain of philosophical truths.
If one would judge, by this standard, Nollet's hypothesis of simultaneous afflux and efflux, and Franklin's hypothesis of positive and negative electricity, I think he would not hesitate long between them.
Nollet, by referring every thing vaguely and indistinctly to afflux and efflux, does not teach us to discriminate any thing; still less, to foresee any thing. He presents a rallying-point for all facts known, or hereafter to be known, but furnishes no clue to guide us out of the labyrinth where they are to be sought. It is as if a botanist should rest satisfied with telling us, that all trees have a trunk, roots, branches, leaves, flowers, and fruits, without teaching us by what features we may recognise such or such a tree, and in what its distinguishing characteristics consist; facts with which it would be more important, however, to make us acquainted, than tediously to repeat these same generalities respecting each individual.
Franklin, in distinguishing between positive and negative elec. tricity, and assigning to each its right place and proper character, so far as the present state of philosophical science admits, diffuses
light far and near, points out the path we must follow in order tɔ make new discoveries, connect them with those already made, extend the limits of science, and make it productive not merely of pleasure but of positive utility. He says; Do this, and such results will follow; change such a circumstance, and such will be the consequences; thus, you can turn such a thing to account; and thus, you may guard against such an inconvenience. You follow his instructions, and every thing takes place in the manner and order that he has pointed out, every thing answers to his views in Europe as in America, and every thing, even the celestial phenomena, demonstrate the soundness of principles, which his modesty suffered him to propose only as mere conjectures.
In a word, I think you will find, as I have done, about the same difference between the theories of these two celebrated electricians, as between the barren and fruitful fig-tree.
On the other hand, it must be admitted, to the honor of the Abbé Nollet, that his electrical experiments on organized bodies, and especially with regard to vegetation and transpiration, are very clear and interesting; and that in this department no one has hitherto surpassed or even equalled him. It were much to be wished, that some good natural philosopher, treading in his steps with the same ardor and skill, would devote himself earnestly to the task of making the most brilliant electrical experiments serve to throw light on various other important points in the animal economy, and especially on the nervous system, the glandular system, the circulation of the fluids, muscular motion, respiration, &c., not only as respects man, but, more particularly, animals of different kinds and orders, (quadrupeds, birds, fishes, reptiles, insects, &c.,) directing electricity by turns on the different organic parts, and under every imaginable variety of circumstances. I should especially desire, that some one would make the experiment, and take all possible care to ascertain, whether, while the internal parts are true conductors, the integuments, at least in most animals, (wool, silk, scales, &c.,) are non-conductors, and to what extent; and whether in this respect, there is much difference, or little, between claws and horns, between hair and wool, &c. I am, Sir, &c.
END OF VOL. V.
FOLSOM, WELLS, AND THURSTON,