Page:Supplement to the fourth, fifth, and sixth editions of the Encyclopaedia Britannica - with preliminary dissertations on the history of the sciences - illustrated by engravings (IA gri 33125011196181).pdf/259

 continents, by the agency of the winds which blow in each;”—a theory which was afterwards adopted by Buffon, and supported with his usual powers of copious and eloquent illustration. In the course of these discussions, Acosta frequently comments upon the opinion of Aristotle, and other ancient philosophers, that the middle zone of the earth was so much scorched by the rays of the sun, as to be destitute of moisture and verdure, and totally uninhabitable. This notion seems to have held its ground in the Schools, even after the discovery of South America had disclosed the magnificent scenery and stupendous rivers of the tropical regions. It appears to have been thought a sort of impiety to question a dogma of such ancient date, and sanctioned by the assent of all the school divines. We learn, from a curious passage in Osborne’s Miscellany of Essays, Paradoxes, and Letters, that the exposing of this ancient error in geography, was one of the circumstances which brought upon the famous Sir Walter Ralegh the charge of general scepticism and atheism. Acosta mentions, that, when he went to America, his mind was deeply imbued with frightful notions of this supposed burning zone, and that his surprise was great, when he beheld it so different from what it had been represented in the “ancient and received philosophy.” “What could I do then,” says he, “but laugh at Aristotle’s meteors and his philosophy?”

Having said thus much in regard to one of the most curious and valuable of the earlier accounts of the new world, it may be proper to add, that, in speaking of the conduct of his countrymen, and the propagation of their faith, Acosta is in no respect superior to the other prejudiced and fanatical writers of his country and age. Though he acknowledges that the carcer of Spanish conquest was marked by the most savage cruelty and oppression, he yet represents this people as the chosen instruments of the Deity, for spreading the truths of the gospel among the nations of America. He accordingly recounts a variety of miracles, as a proof of the constant interposition of Heaven, in favour of these merciless and rapacious invaders. It will appear from the following curious passage, that he even makes the great enemy of mankind himself, a co-operator in that scheme of conversion for which he represents the Spaniards to have been predestined. “That” says he, “which is difficult in our law to believe, has been made easy among the Indians; because the Devil had made them comprehend even the self same things, which he had stolen from our evangelical law,—as their manner of confession, their adoration of three in one, and such like; the which, against the will of the enemy, have holpen for the easy receiving of the truth.”

Besides his History, Acosta wrote the following works: 1. De Promulgatione Evangelii apud Barbaros.—2. De Christo Revelato.—3. De Temporibus Novissimis, libros vi.—4. Concionum, tomos iii. All of these works were, in their day, frequently reprinted; but it is only by his history that his name is now known in the literary world. The English translation, from which we have taken the preceding extracts, was published at London, in quarto, in the year 1604, and is now rather a scarce book. ACOUSTICS. The doctrine of sound is unquestionably the most subtle and abtruse in the whole range of physical science. It has given occasion, in recent times, to much controversy and disenssiondissension [sic], and has eventually called forth all the mighty resources of a refined and elaborate calculus. Yet an evident obscurity still remains to overcloud the subject. The discrepancies between theory and observation have been made entirely to disappear from astronomy, which has at last attained a degree of perfection befitting the sublimity of the science. But some latent suspicions pervade the structure of acoustics, sufficient to disturb that feeling of confidence which is calculated to invigorate our pursuits. The general theory of sound, and its application to a variety of curious philosophical amusements, have been explained in the body of the work. We purpose, however, to reconsider the subject at large, and to examine closely the bases on which it rests. But we must content ourselves at present with a few sketches, reserving our extended remarks for their several distinct heads, in hopes that, during the progress of this Supplement, we shall be able to collect more accurate and complete materials.

The impression of sound is conveyed by means of a certain tremor or internal agitation, which shoots, with more or less celerity and force, through any substance, whether solid or fluid. Nor is it requisite that the conducting medium should belong to the class of bodies which are commonly denominated elastic. In fact, all bodies whatever, in the minute and sudden alterations of their form, exert a perfect elasticity, and only seem to want this energy when they undergo such great changes, that their component particles take a new set or arrangement, which prevents the full effect of reaction.

It is not every kind of tremulous motion, however, that will excite the sensation of sound. A certain degree of force and frequency in the pulsations appears always necessary to affect our sense of hearing. Yet the impression of sound is not confined to the mere external organ; the auditory nerves have a considerable expansion, and sympathize with those of taste and of smell. The only inlet of vision is by that very narrow aperture, the pupil of the eye; but the reception of sound partakes more of the character of the general sense of feeling, which, though most vivid at the extremities of the fingers, is likewise diffused over the whole surface of the body. The intimation of the car is accordingly assisted by the consent of the palate, the teeth, and the nostrils. Fishes hear very acutely under water, though the organ itself lies so concealed in the head, as to have long escaped the diligence of anatomists.

It was formerly supposed, that the transmission of impulse through a solid body is perfectly instantaneous. This formed, indeed, one of the Cartesian tenets, which Newton himself has tacitly admitted. But accurate observations have since proved, that motion is always really progressive, and propagated in succession. Professor Leslie has shown that the darting of impact through any substance, whether hard or soft, is accomplished by the agency of the same interior mechanism as that of sound, and has