In Mr. Ross’ translation of Dr. Tschudi’s Travels in Peru, 1847, we are informed that the correct orthography is Huanu, and not Guano. He states that it is a term in the Quichua dialect, meaning “animal dung.” As the word is now generally used it is an abbreviation of Pishu Huanu, bird dung. “The Spaniards,” he says, “have converted the final syllable nu into no The European orthography Guano, followed also in Spanish America, is quite erroneous, for the Quichua language is deficient in the letter G, as it is in several other consonants. The H, in the common formation of the word, is strongly aspirated, whence the error of the orthography of the Spaniards, who have sadly corrupted the language of the Autochthones of Peru.”
What is Perspective?
Perspective is the science which furnishes us with the laws by which we can give the apparent, as geometry those by which we can give the real, forms of objects. These laws are obvious without rules to thoughtful, artistic common-sense—but, to many, books on the subject will always be useful, if not indispensable. The science was called perspective, or seeing through, from an impression that the correct foreshortening of objects could be gained by viewing and tracing them through a pane of glass. This plan only ensures correctness when the plane of the eye is parallel to that of the medium upon which the drawing is made. A picture in perspective is simply a plane parallel to the plane of the eye intersecting the rays that come from the surface of the objects represented. The points of these rays at the places of their several intersections combine to form the true perspective representation. This was the art that Mantegna made so much of at Padua; and that with which Bellini, the painter of the National Gallery “Doge,” delighted the Venetians. Without much semi-scientific pedantry, the whole science may be understood by balancing a half-crown on the top of the forefinger of your right hand. Hold it up so that its broad plane is parallel to the eye’s plane; put it nearer or further, and it seems to increase or diminish in size. Turn it obliquely, and it appears an oval; put the edge on a line with the eye, and it appears a mere thin straight line. A sphere is the only geometric form that undergoes no perspective changes. The eye is able to take in any given space set at an angle of under sixty degrees. When both eyes view a scene, instead of the circle one eye sees, we have an ellipse formed by the continuation of the two circles of vision,—the point of sight being opposite the centre of the space between the two eyes. Perspective is of great use in Art; but the books upon it are too abstruse, and imply a knowledge of mathematics. [This common-sense explanation is from the pen of Professor Wallace, M.A., in the first number of a journal edited by him and entitled The Public Instructor.]
The Stereoscope.
Till the discovery of the Stereoscope, naturalists were puzzled to account for a single image resulting from double vision; and Gall and Spurzheim endeavoured to explain it by the supposition that one eye only was active at a time, the other only admitting light, and that Nature had given us two merely to provide against the accidental loss of one.—Leslie’s Handbook.
Burning Lenses.
The danger from Lenses, when the heat of the sun is powerful, is well known. As an illustration, we may relate an instance which occurred on the premises of Messrs. Negretti and Zambra, philosophical instrument makers, in Hatton Garden. There was a smell of fire, but it could nowhere be detected, until a person entered the shop from the street with the startling information that the window was on fire, and such was really the fact: a large reading-lens hanging in the window exposed to the sun, its focus happening to be just within range of the woodwork of the window fittings, set fire to them, and no doubt in a very few seconds some serious damage would have been caused. Is it not possible that in tropical climates, when vessels are becalmed, they may be set on fire by the eye-deck lights everywhere observable on ships’ decks; or, nearer home, in warehouses, &c., where such means of lighting is resorted to? The matter merits serious consideration and should serve as a caution.
How to wear Spectacles.
In the proper use of Spectacles there is no circumstance of more importance than their position on the head. They should be worn so that the glasses may come as close to the eye as possible without touching the eyelashes; they must also be placed so that the glasses may be parallel to the paper when held in an easy position. To accomplish this, let the sides of the spectacles bear upon the swell of the head, about midway between the top of it and the ear; the eyes will then look directly through the glasses to the paper, and make the most advantageous use of them, instead of looking obliquely through them to the paper, as in numerous cases, where persons place the sides of their spectacles in contact with, or very near, their ears—in which position they produce a distorted image on the retina. The sides of the spectacles should also be placed at an equal height upon the head; and the hands being applied to the points of the sides, will generally direct their equal height, as well as allow of their opening to the full extent without injury.—Adams on the Human Eye.