Obrázky na stránke
PDF
ePub
[ocr errors]

66

“The art of engraving on metal, and of printing with the rol, ling press, is supposed to have been invented in the year 1423. "Some attribute the art of printing with types to Laurentius "Coster, of Haerlem, who, as they say, in 1430, employed for the purpose separate blocks of wood, tied together with thread. "Genstleich, one of his workmen, went to Mentz, and was there "assisted by Gutenberg, who invented types of metal. But the "best authors appear to disbelieve this story; and Gutenberg, in (6 partnership with Fust, and Schoeffer, is the first that is univer. ૨૮ sally allowed to have practised the art. It was introduced into this country by William Caxton."

[ocr errors]

"Leonardo da Vinci, the most accomplished man of his age, 66 was born about the year 1443, and excelled not only in painting "and poetry, but also in architecture, mathematics, and mechanics. "The state of practical mechanics in this and the subsequent cen"turies may be estimated from Ramelli's collection of machines, "which contains several curious and useful inventions; some of them long since forgotten, and even lately proposed again (6 as new,'

[ocr errors]

"The works of Bacon, Lord Verulam, although not immediately tending to the advancement of mathematics or mechanics, "are universally allowed to have conduced very materially to the "improvement of every branch of science, by the introduction of a correct and conclusive method of philosophical arrangement "and inquiry. Guido Ubaldi published, in 1577, a treatise on "mechanics, not wholly exempt from inaccuracies; and in the fol"lowingyear, a valuable commentary on the works of Archimedes:

[ocr errors]
[ocr errors]
[ocr errors]

66

some of the properties of projectiles were about the same time "rather imagined than demonstrated by Tortalez: Benedetti soon "after began to reason correctly respecting the principles of me"chanics; but it was reserved for Galileo to lay the foundations "of the discoveries, which have succeeded each other with increa sing rapidity for more than two centuries. He investigated, in "the year 1589, the laws of accelerating forces, and shewed the nature of the curve which is described by a projectile he infer. "red from observation the isochronism of the vibrations of a pen. ❝dulum, and the principle was soon after applied by Sanctorius "to the regulation of timekeepers. Stevinus, a Dutchman, was "the first that clearly stated the important law by which the equi"librium of any three forces is determined: and the properties "of the centre of gravity were successively investigated by Lucas "Valerius, Lafaille, and Guldinus, who made some additions to "the elegant propositions of Archimedes which relate to it."

Should it be asked, which of the lectures of the second division seem to be written with more particular attention, an

less any one wish to examine the authors themselves for any very particular purpose, he need not take any farther trouble; for the abovementioned statements are clearly and accurately expressed, so as to afford complete satisfaction.

The division on Friction, which follows the above, contains an elegant abstract of Coulomb's memoir on Friction.

The reader will be enabled to form a better idea of the manner in which Dr. Young expresses the result of experiments, by the following specimen, which has been transcribed from page 185:

"From the Journals of the Royal Institution. Extract from 66 a Memoir of M. Labillardière, on the Strength of the "Fibres of the Flax of New Zealand. Read before the "National Institute. B. Soc. Phil. n. 75.

"This flax, the phormium tenax, was procured from the inha, "bitants of New Zealand, by M. Labillardière himself, in the 66 voyage he made in search of La Peyrouse.

"In these experiments particular care was taken to employ substances of a diameter as equable as possible throughout their "lengths. The inferences are, that the strength of the fibres of the 66 great aloe, agave Americana, being equal to 7, that of common "flax is represented by 112; that of hemp by 164; that of the "flax of New Zealand by 23; and that of silk by 34. If we "call the strength of the flax 1000, that of the aloe will be 596, "of hemp 1390, of the phormium 1996, and of silk 2894.

"The degree of extension of these fibres, before they break, is "in a different proportion. Supposing it 1 for flax, it is 2 for 66 hemp, 3 for the flax of New Zealand, 5 for the agave, and 10 for ❝ silk. It is well known, that the strength of cords depends as "well on their elasticity, as on the ultimate force required to break them.

"The experiments and reflections of M. Labillardière, shew "beyond contradiction, that many advantages may be obtained "from the cultivation of this flax on a large scale; and that it may be attempted with a prospect of success in the southern parts "of France."

[ocr errors]

A list of elegant and useful particulars, contained in this part of the work, might be protracted to an immense length, but it will be sufficient to add one specimen more of this author's style; which gives an account of experiments and ob

servations on the height of falling or shooting stars; by Benzenberg and Brandes.

"They were observed, (he says,) from a base of 46200 feet F. or "2 German geographical miles, 15 of which make a degree: their "height was from 4 to 30 of those miles; the mean height about 11, or near 50 English miles; the velocity of two of them was " from 4 to 6 miles, or about 22 English miles in a second. One 66 was brighter than Jupiter, and was 450 miles distant.

66

[ocr errors]

"In the second paper Dr. Benzenberg gives two instances in "detail.-September 15. A shooting star of the fifth magnitude. "Elevation of the beginning 7,7 geographical miles of the end "8,2. Length of the path, 1,5 miles. Longitude of the place "of disappearance 28° 3'. Latitude 53° 22'. Observed by Bran "des, in Ekwarden, and Benzenberg, in Ham, near Hamburgh: length of the base 14 miles. -October 3. Another of the fourth 66 magnitude observed by the same persons. The termination 7,1 "geographical miles above the earth. Longitude 27° 7'; lat. 53°5'. These observations shew, says Dr. Benzenberg, that a (6 long base will furnish as accurate a comparison as a shorter one; "that even meteors of the fourth and fifth magnitude, may be seen "at places distant above 14 geographical miles from each other; "and they confirm the former observations made at Gottingen with 66 a base of but one or two miles. Dr. Pottgiesser, in Elberfeld,

40 miles distant from Hamburgh, saw a meteor on the 2d of Oc66 tober, in the zenith, which appears to have been the same as was 66 seen at Hamburgh in the horizon; its height is estimated at 25 "German miles. It was intended to continue these observations "with unremitting assiduity."

The eleven papers, which follow the catalogue of references, had all been published before, principally in the Philoso hical Transactions; but in the present volume they have been reprinted with various corrections.

The first paper, under the title of Observations upon Vision, treats of the manner in which the eye accommodates itself to view objects distinctly at different distances :-a subject which has exercised the ingenuity of the most able physiologists. Dr. Young, in the first place, briefly describes the theories, or hypotheses, of Kepler, Descartes, De la Hire, Dr. Pemberton, Dr. Potterfield, Dr. Jurin, Musschenbrock, and others; then subjoins the account of his discovery relative to the construction of the crystalline lens of the eye of the ox, and gives a minute

[ocr errors]

description of that lens: upon which he establishes his theory of the accommodation of the eye for distinct vision of objects placed at different distances. In the latter part of the paper, this author answers the following queries: 1st, What is the cause of the lateral radiation which seems to adhere to a candle viewed with winking eyes? 2d, Whence arises that luminous cross, which seems to proceed from the image of a candle in a looking-glass? 3d, Why do sparks appear to be emitted when the eye is rubbed or compressed in the dark? But the statement of the abovementioned theory, and the answers to the three queries, cannot be rendered intelligible, without the previous description of the crystalline lens; but the insertion of the whole in the present account would protract it to too great a length. A plate is annexed to this paper, which exhibits a vertical section of the ox's eye, and the structure of the crystalline, with a side-view of the same.

The title of the second paper is, Outlines of Experiments and Enquiries respecting Sound and Light. Those particulars are arranged in sixteen divisions, and the experiments, and the deductions from those experiments, as they are described in the sections, though not always conclusive, are, however, very ingenious, and most of them are deserving of farther attention. -Five copper-plate engravings, with a variety of figures, belong to this paper.

Of the contents of the remaining papers, it is not practicable to give a concise and satisfactory account.

The last article of the work is an ample and accurate index, which occupies not less than 56 pages, and refers to both volumes. By the assistance of this index, the present work, which contains an immense variety of particulars, is rendered nearly equivalent to a philosophical dictionary.

The preceding account may probably be presumed to give the reader a pretty just idea of Dr. Young's present work, an examination of which has here been humbly attempted. But should a more definite statement of its merit be demanded in a

[ocr errors]

few words, a satisfactory answer might perhaps be given by saying, that Doctor Young's two volumes, intitled A Course of Lectures, &c. form rather a collection of that author's dif ferent works, than a uniform or homogeneous performance; nor can it be denied, that the execution of the different parts exhibits a considerable inequality. But taking it altogether, it must undoubtedly be considered as being a very ample, an elaborate, an accurate, and a most useful, repository of Natural Philosophy in its present state, as well as of several collateral branches of knowledge.

[ocr errors]
[blocks in formation]

IT is generally believed, that Fashion is most despotic in those countries, where the greatest progress has been made towards civilization and refinement. This is not the case. In the wilds of Africa, on the frozen mountains of Lapland, over those vast and solitary plains, where the Arab and Tartar roam, in those regions where the human mind dozes under the narcotic influence of Mohammedan power,-wherever, indeed, barbarism and ignorance prevail, Fashion reigns with absolute dominion; and the laws, which she established some thousand years ago, are still observed with religious reverence. The slightest attempt at innovation is regarded with horror, and the abolition or alteration of the most trivial custom, which Fashion has consecrated, might cause the revolution of empires. But as the light of reason becomes diffused, and arts and sciences begin to be cultivated, the sanctity of peculiar modes, to which antiquity had imparted an appearance of inviolability, is gradually invaded; till at length

« PredošláPokračovať »