« IndietroContinua »
But to return to the essay: he observes “ Although the atmosphere is usually termed a fluid, yet from several peculiarities observable in its nature, some philosopher's appear to have entertained doubts upon this subject; Mr. B. Martin, in his lectures calls it a fluid “ sui generis.” Air is observed to differ froin other fluids, first in not possessing the property of congelation, and secondly, from its not being uniformly dense throughout.”
This displays the grossest ignorance of the present state of experimental philosophy. The notion that air is not a fluid, is cqually repugnant to science and to common experience, and the most received ideas, or definitions of fluidity. The author is not to be excused, for citing a surmise so absurd. Nor is he less amenable for quoting the opinion of Mr. Martin, uttered a
" that the air is a fluid sui generis,” were the originator recalled into existence, he would blush to repeat it after the slighest review of the luminous discoreries of the modern chemists.
It is now well known, even to school boys, that the atmosphere is composed of two species of air, which both in their chemical, and mechanical properties, so far coincide with other permanently elastic fluids, as to justify a generic classification under the term gas.
The author next observes, “ It may perhaps be urged in objection to the truth of the assertion that air does not possess the qualities of fixation; that whenever it becomes one of the component parts of a natural body, it is in that situation found to be in a fixed state; this objection is frivolous; and to obviate it we have only to recollect that when air becomes a part of any body, it docs [not] in so doing take a material form, but is, while so situated, merely in a state of confinement."
Air does not differ from all other fluids in being variable, or unequable in its density. This characteristic appertains to all clastic fluids, among which we may comprise steam, and all other vapours, also caloric, light, and the electric fluid. The latter part of the last quotation is contradictory. How can air become a part a body, and not become fixed in it? Some carbonates contain 12 를 or of their hulk of fixed air, or carbonic acid gas. It may
perhaps be said with propriety, that when the principles constituting air become solid, or a part of a solid, they cease to be air. It is however well understood, that by the phrase fixation of air, the idea is conveyed of the condensation of its principles into the solid form without decomposition. Thus the muriatic acid gas, and the ammoniacal gas, meeting, they are condensed into muriate of ammonia, or sal ammoniac, without any loss of any of their component parts.
Soon after the above, we are informed that the barometer ascertains heights with astonishing accuracy.
It is known to all familiar with the barometer, that it only indicates the weight of the superincumbent atmosphere. Now this being notoriously liable to vary, from other causes than change of elevation, the range or possibility of error is obviously equal to the possible extent of those other causes. The remarks of this essayist on the thermometer, , are still
He informs us, that cold of tolerable intensity, is sufficient to freeze spirit of wine (page 440.) It is well known that this fluid, which is in science denominated alcohol, has never exhibited the slightest symptom of congelation in the extremest cold. Of this the author might have informed himself, had he perused any modern elementary work upon chemistry; and more especially that of Thomson, which is now in the hands of almost every student in natural science.
“Alcohol is exceedingly fluid, and has never been frozen though exposed to a cold so great as 69. Indeed Mr. Walker sunk a spirit of wine thermometer to 9 1 without any appearance of congelation. (Thomson's Chemistry, 3d edition, vol. 2, page 580.) Mercury freezes at 39, and yet our philosopher would assign its more difficult congelation as a motive for preferring it to alcohol in the fabrication of thermometers.
I hope the author will excuse these hints, and that they will induce him in future to read more, and write less.
RHETORIC-FOR THE PORT FOLIO.
Of the constituent parts of a regular discourse; with exemplifications of the
different kinds of public Speaking.
In every species of composition there are certain rules adapted to the proper or scientific arrangement of its respective parts. When such rules are neglected it will be rendered crude and uninteresting to a common, and to a classical ear, vapid and offensive; though decorated occasionally with the most brilliant ornaments of language, and communicated with all the dignity and expression of chaste and animated eloquence.
Order, or regularity of arrangement and symmetry constitute the foundation of beauty as much in intellectual as in material productions, and the exercise of skill in the construction of an oration or poem, is as essential to its perfection, as it is to the perfection of any thing produced by the exercise of the mechanic arts.
Our attention is particularly called, this evening, to the constituent parts of a rezular discourse or oration. These have been considered by rhetoricians as reducible to six heads, viz. Exordium, Narration, Proposition, Confirmation, Refutation, and Peroration, or Conciusion: where these are observed in the order I have mentioned, the discourse must be complete with respect to its form; its intrinsic merit or demerit will arise from the sentiments conveyed, the author's style or manner of thinking, and the language or channel through which his sentiments are communicated.
Orations may be considered of three kinds, viz. demonstrative, deliberative, and judicial. Of the demonstrative kind are philosophical discussions, panegyrics, culogiums,epithalamiums, congratulations, &c. To the deliberative belong persuasion, exhortation, &c. And to the judicial, accusation, confutation, &c.
1. The Exordium or beginning of an oration, is that part of it in which we should inform our audience of the nature of the
subject we mean to offer to their attention, and endeavour to conciliate their favour, by mentioning any recommendatory circumstances by which it is rendered peculiarly interesting; and at the same time to deprecate their censure by suggesting any reasons in extenuation of its imperfection. In doing this, however, the speaker should be brief, perspicuous, modest, and explicit; his mode of delivery mild, respectful, and deliberate; and his tone of voice so accommodated to the size of the building and extent of the audience as merely to be heard distinctly, thereby reserving the strength and power of his voice to give the necessary expression to the subsequent and more interesting parts of his address.
2. Narration is a recital or rehearsal of the facts upon which the address is founded, including a statement of the cause, manner, time, place, and consequences of the action. This should necessarily be as short as perspicuity will permit, lest the attention of the hearer should be fatigued before he is called upon to consider the arguments which may be offered in support of the case.
Great regard should also be paid to clearness in the arrangement of the incidents, as the strength of the Confirmation will very much depend upon the proper management of the Narration.
In pronouncing the Narration, the voice should be more elevated, the gesture more expressive, and the general air of the speaker more animated. The ease and gracefulness which renders a narration so pleasing in common conversation, will excite in the hearer a superior delight when exhibited by a public speaker, who accompanies his communication with appropriate action and expression of countenance.
3. Proposition-The intention of the speaker in every correct and regular address is to prove or illustrate something:
The proposition therefore is an explanation of the purport or sum of the whole discourse or thing in dispute.
When the subject relates to several different points, cach of which must be stated in a distinct proposition, it is called partirion. When the speaker inforios his hearers of the several parts of his intended discourse, it is called enumeration; and these should never exceed three or four at most.
The chief things to be attended to in delivering the proposition or subject of the discourse, are, distinctness of articulation, fulness of tone, and a considerable degree of deliberateness.-The intention being merely to inform the mind of the hearer, without any appeal to his imagination or his passions, ther: cannot be much occasion either for variety of tone or energy
of action. 4. Confirmation is that part of the oration which contains the illustrations, proofs, or arguments, adduced to inforce or confirm the proposition. Some addresses indeed require nothing more than an enlargement or illustration to place those proofs in a proper light, and so forcibly to recommend their subject as to produce conviction of its truth and propriety in the minds of the hearers : in such cases a distinct proposition is rendered unnecessary, and of course confirmation is thereby rendered so, that properly consisting of arguments brought in defence of the proposition. Ilence Cicero defines confirmation to be "thať which gives proof, authority, and support to a cause by reasoning”-and this is effected by different modes, according to the nature of the subject, and the character who handles it: the logician directing his arguments in a different channel from the mathematician, or the professed orator. Let the inocle or form however of the argument be what it may, it must belong either to the Synthetic or the Analytic method of reasoning: the former beginning with the parts and combining them gradually into the whole, as in treating of grammar we begin with orthography, or the nature and power of letters and syllables, and proceed to Etymology, Syntax, and Prosody--the latter, i. e. the Analytic, taking the whole compound as we find it and resolving it into its parts, as when we resolve a discourse into its several heads.
In this part of our address rhetoricians advise that the strongest arguments should be placed in the front or at the beginning, the weakest in the middle, and that some few of the best be kept for the conclusion, as a corpse de reserve. (vide Cic. de Ora. 2. 27.)
Here the speaker is required to increase both his voice and gestures, as he will naturally be more carnest to recommend his