Page:The American Cyclopædia (1879) Volume XI.djvu/26

 18 MAGNETO-ELECTRICITY periment be one of soft iron and sud<l< j a -al aiiic current, the popper disk pre- viously put in rapid motion will instantly be topped. Tin- current in the radii of the plate which an- approaching the magnetic pole, being ppoflfee direction to those in the magnet, will In- repelled ; while those in the radii on the other ride of the p<-lc, l.-in^ in the same direc- tion with the current in the magnet, will be at- tracted ; and hence the resultant action of all the induced currents will he to stop the plate. A himilar rc-ult is produced when a cube of cop- ahoiit an inch in diameter is suspended between the poles of a powerful electro-magnet, and caused rapidly to revolve, from the un- _r ..f a thread hy which it is suspended; when th- magnet is suddenly excited, the revo- lutinn ( .f the cube is instantaneously arrested, and brought to rest without the least oscillation, l ni momentum and consequently the iner- tia of the mass were instantly annihilated. If, in tin- case of the arrangement of the revolving disk wt: 1 1 a vi- mentioned, a rapid motion be communicated to it hy a train of wheels in op- po*ition to the resistance between the induced 1 currents and the magnet, a considerable exer- tion will be required to continue the motion ; and since, according to the principle of the con- servation of force, tin muscular power expend- ed must produce some effect, and no change is found in the condition of the metal after the experiment, the conclusion was drawn that the energy exerted was expended in generating heat, the truth of which was established by Foucatilt. The disk thus made to revolve in op- position to the force of the magnet increases in temperature, and soon becomes sufficiently hot to set fire to an ordinary match. The Magnet- ism induced from the Earth and the Sun. The earth being a great magnet, currents of elec- tricity HUM he induced in all conducting ma- terial in which motion takes place at its surface. These curn-nN are, however, of feeble intensity, but their existence may be shown by connect- ing the ends of a copper wire several hundred yard- in h-nirth. cov.-r.-d with silk and wound around a w I n cylinder of about 2 ft. in with a galvanometer, and by suddenly turning tin- -'^i- of th,- former from ahorizontal D into the direction of the dipping needle. Daring the downward motion of the. X. end of the cylind.T, the LMlv.iriom.-t.-r will indicate an 1 current in an opposite direction to that of the hypothetical current of the earth, and, w-hen the motion is reversed, an induced cur- r ' -tlt in 'he n ! -, t ;,.n as that of the current in the earth. From this result it must be in- ferred that elect rieal eurreiits are constantly d hy tin- ma/m-t im of the earth, since i th.- direction and position of a an take place without devel- ! inductive action. Moreover, >im-r i has been proved i" he a <rreat magnet, t-xcrting a powerful action on the ear'h. the i of th.- lattermust object it to an inductive m-tioM. -imilar to that we have de- MAGXOLIA scribed in the revolving plate of copper. There can be no doubt, in the present state of science, that such currents actually do take place, but their direction and intensity have not yet been ascertained. But from the association of the magnetic storms we have previously described with the occurrence of the aurora borealis, and also with that of the maximum number of spots on the sun, we are led to the conclusion that the three classes of phenomena are inti- mately connected, and that they furnish a sub- iect of cosmical research of perhaps as great interest as any which have ever occupied the attention of the scientific world. MAGMFYIXG GLASS. See MICROSCOPE. MAGXIN, Charles, a French author, born in Paris, Nov. 4, 1793, died there, Oct. 7, 1862. He received a brilliant education, and became in 1813 assistant in the imperial library, and in 1832 one of the directors of that institution. His theatrical criticisms in the Globe (1826- '30), his lectures at the Sorbonne (1834-'5) on the origin of the modern stage, and his various writings won for him the praise of Sainte- Beuve, and a seat in the academy of inscrip- tions and belles-lettres. He also wrote poetry and plays. His principal works are : Oritjiius du theatre moderne (1838) ; Cauteries et medi" tations (2 vols., 1843) ; Theatre de Hroswitlia (1845, with text and translation) ; and Histoire des marionettes (1852). MAGOLIA, a genus of trees and shrubs dedi- cated by Linnaeus to Pierre Magnol, professor of botany at Montpellier, France, at the close of the 17th century, and who was the fir?t to apply the term " family " to designate groups of botanical genera. The genus is the type of the Magnoliacece, a family as to the limits of which botanists are not agreed ; as accepted by Bentham and Hooker (Genera Plantaruni), it includes nine genera, four of which, Magnolia, liriodendron, illicium, and schizandra, are rep- resented within the United States. In Mag- nolia there are fourteen species, six of which belong to Japan, China, and the Himalayas y and the remainder to North America, including Mexico. While a few are low shrubs, the ma- jority are fine trees, some reaching the height of 50, 60, and even 100 ft. ; there are both evergreen and deciduous species, and nearly all are ornamental by reason of their fine foli- age and flowers. The leaves are alternate, sometimes so crowded upon the stem as to ap- pear whorled, entire, furnished with stout pe- tioles, which when they fall leave broad scars upon the stems ; the leaves proceed from cylin- drical, acute buds, the integuments or protect- ing bud scales of which consist of the large deciduous stipules, which are adherent to the base of the petioles ; the stipule of each leaf envelops the succeeding leaf next above it, which is folded lengthwise and rests against the next stipular sheath, and so on ; the stipules fall away as the leaves unfold. The flowers, usually large, are solitary and terminal, and are white, greenish yellow, or purple; they