In order to realize the production of these fields, several means can be employed: The current is sent from an alternating current machine into the primary circuit of a transformer and thence into one of the bobbins, the other being supplied by means of the secondary current of the transformer. A resistance introduced into the circuit will produce the required difference of phase, and the equality of the intensities of the fields will be obtained by multiplying the number of turns of the secondary wire on the bobbin. Moreover, the two bobbins may be supplied by the secondary current of a transformer by producing the difference of phase, as in the first case.
In the motor constructed by Prof. Ferraris the armature consisted of a copper cylinder measuring 7 centimeters in diameter and 15 centimeters in length, movable on its axis. The inductors were formed of two groups of two bobbins. The bobbins which branched off from the primary circuit of a Gaulard transformer, and were connected in series, comprised 196 spirals with a resistance of 13 ohms; the bobbins comprising the secondary circuit were coupled in parallel, and had 504 spirals with 3.43 ohms resistance. In order to produce the difference of phase, a resistance of 17 ohms was introduced into the second circuit, when the dynamo produced a current of 9 amperes with 80 inversions per second. Under these conditions the available work measured on the axis of the motor was found for different speeds: Revolutions per minute: 262—400—546—650—722—770. Watts measured at the brake: 1.32—2.12—2.55—2.77—2.55—2.40. The maximum rendering corresponds to a speed of rotation of 650 revolutions, and Prof. Ferraris attributes the loss of work for higher speeds to the vibrations to which the machine is exposed. At present the apparatus is but a laboratory one.—Bulletin International de l'Electricite.
THE ELECTRIC AGE.
By Charles Carleton Coffin.
The application of electricity for our convenience and comfort is one of the marvels of the age. Never in the history of the world has there been so rapid a development of an occult science. Prior to 1819 very little was known in regard to magnetism and electricity. During that year Oersted discovered that an electric current would deflect a magnetic needle, thus showing that there was some relationship between electric and magnetic force. A few months later, Arago and Sir Humphry Davy, independently of each other, discovered that by coiling a wire around a piece of iron, and passing an electric current through it, the iron would possess for the time being all the properties of a magnet. In 1825 William Sturgeon, of London, bent a piece of wire in the form of the letter U, wound a second wire around it, and, upon connecting it with a galvanic battery, discovered that the first wire became magnetic, but lost its magnetic property the moment the battery was disconnected. The idea of a telegraphic signal came to him, but the electric impulse, through his rude apparatus, faded out at a distance of fifty feet. In 1830 Prof. Joseph Henry, of this country, constructed a line of wire, one and a half miles in length, and sent a current of electricity through it, ringing a bell at the farther end. The following year Professor Faraday discovered magnetic induction. This, in brief, is the genesis of magnetic electricity, which is the basis of all that has been accomplished in electrical science.
The first advance after these discoveries was in the development of the electric telegraph—the discovery in 1837, by the philosopher Steinhill, that the earth could serve as a conductor, thus requiring but one wire in the employment of an electric current. Simultaneously came Morse's invention of the mechanism for the telegraph in 1844, foreshadowed by Henry in the ringing of bells, thus transmitting intelligence by sound. Four years later, in 1848, Prof. M. G. Farmer, still living in Eliot, Me., attached an electro-magnet to clockwork for the striking of bells to give an alarm of fire. The same idea came to William F. Channing. The mechanism, constructed simply to illustrate the idea by Professor Farmer, was placed upon the roof of the Court House in Boston, and connected with the telegraph wire leading to New York, and an alarm rung by the operator in that city. The application of electricity for giving definite information to firemen was first made in Boston, and it was my privilege to give the first alarm on the afternoon of April 12, 1852.
At the close of the last century, Benjamin Thompson, born in Woburn, Mass., known to the world as Count Rumford, was in the workshop of the military arsenal of the King of Bavaria in Munich, superintending the boring of a cannon. The machinery was worked by two horses. He was surprised at the amount of heat which was generated, for when he threw the borings into a tumbler filled with cold water, it was set to boiling, greatly to the astonishment of the workmen. Whence came the heat? What was heat? The old philosopher said that it was an element. By experiment he discovered that a horse working two hours and twenty minutes with the boring machinery would heat nineteen pounds of water to the boiling point. He traced the heat to the horse, but with all his acumen he did not go on with the induction to the hay and oats, to the earth, the sunshine and rain, and so get back to the sun. One hundred years ago there was no chemical science worthy of the name, no knowledge of the constitution of plants or the properties of light and heat. The old philosophers considered light and heat to be fluids, which passed out of substances when they were too full. Count Rumford showed that motion was convertible into heat, but did not trace the motion to its source, so far as we know, in the sun.
It is only forty-six years since Professor Joule first demonstrated the mutual relations of all the manifestations of nature's energy. Thirty-nine years only have passed since he announced the great law of the convertibility of force. He constructed a miniature churn which held one pound of water, and connected the revolving paddle of the churn with a wheel moved by a pound weight, wound up the weight, and set the paddle in motion. A thermometer detected the change of temperature and a graduated scale marked the distance traversed by the descending weight. Repeated experiments showed that a pound weight falling 772 feet would raise the temperature of water one degree, and that this was an unvarying law. This was transferring gravitation to heat, and the law held good when applied to electricity, magnetism, and chemical affinity, leading to the conclusion that they were severally manifestations of one universal power.—Congregationalist.