CHAPTER XLI.

WE may avail ourselves of the space here afforded to note briefly a few of the features of the progress of physical science in recent times. It has now been perceived that the sources of human happiness lie far removed from the fictitious splendors of public life. History is departing more and more from the methods of the old annalists to depict the movements of human thought and the adaptation of the physical means of amelioration and progress. It is safe to aver that the recent additions by inventive processes to the resources of physical happiness are the most striking and valuable feature of the civilization of our times. At no other age in the history of the world has a practical knowledge of the laws of nature been so widely and so rapidly diffused. At no other epoch has the subjection of natural agents to the will of man been so wonderfully displayed. The old life of the human race is giving place to a new life based on scientific research and energized by the knowledge that the conditions of our environment are as benevolent as they are unchangeable.

It has remained for American genius to solve the problem of oral communication between persons at a distance from each other. The scientists of our day, knowing the laws of sound and electricity, have devised an apparatus for transmitting the human voice to a distance of hundreds, or even thousands, of miles. The TELEPHONE must stand as a reminder to after ages of the genius and skill and progress of our country in the last quarter of the nineteenth century.

This instrument seems to have been the work of several ingenious minds directed to the same problem at the same time. The solution of the problem, however, should be accredited to Elisha P. Gray, of Chicago, and Alexander Graham Bell, of the Massachusetts Institute of Technology. It should be mentioned also that Amos E. Dolbear, of Tufft's College, Massachusetts, and Thomas A. Edison, of New Jersey, likewise succeeded in solving the difficulties in the way of telephonic communication, or at least in answering practically some of the minor questions in the way of

success.

The telephone is an instrument for the reproduction of sound, particularly of the human voice, by the agency of electricity, at long distances from the origin of vocal production. The phenomenon called sound consists of a wave agitation communicated through the particles of some medium to the organ of hearing. Every particular sound has its own physical equivalent in a system of waves in which it is written. The only thing, therefore, that is necessary in order to carry a sound in its integrity to any distance, is to transmit its physical equivalent and to redeliver that equivalent to some organ of hearing capable of receiving it.

Upon these scientific principles the telephone has been produced. Every sound which falls upon the sheet-iron disk of the instrument communicates thereto a sort of tremor. This tremor causes the disk to approach and recede from the magnetic pole placed just behind the diaphragm. A current of electricity is thus induced, pulsates along the wire to the other end, and is delivered to the metallic disk of the second instrument many miles away just as it was produced in the first. The ear of the hearer receives from the second instrument the exact physical equivalent of the sound or sounds which were delivered

against the disk of the first instrument, and thus the utter ance is received at a distance just as it was given forth.

The telephone stands to the credit of Professors Gray and Bell. Long before their day, however, some of the principles on which the instrument has been created were known. As early as 1837 the philosopher Page succeeded in transmitting musical tones to a distance. Forty years afterwards, namely, in 1877, Professor Bell, in a public lecture at Salem, Massachusetts, astonished his audience and the whole country by receiving and transmitting vocal messages from Boston, twenty miles away. Incredulity was dispelled in the face of the fact that persons far away were actually conversing with each other by means of the telephone. The experiments of Gray at Chicago, only a few days later, were equally successful. Messages between that city and Milwaukee, a distance of eighty-five miles, were plainly delivered. Nor could it be longer doubted that a new era in the means of communication had come.

The telephone was soon followed by the PHONOGRAPH. Both inventions are based on the same principle of science. The discovery that every sound has its physical equivalent in a wave or agitation led almost inevitably to the other discovery of catching, or retaining, that equivalent, or wave, in the surface of some body, and to the reproduction of the original sound therefrom.

The phonograph consists of three principal parts: the sender, or funnel-shaped tube, with its open mouthpiece, standing toward the operator; the diaphragm and stylus connected therewith, which receive the sound spoken into the tube; and the revolving cylinder, with its sheet coating of tinfoil laid over the surface of a spiral groove, to receive the indentations of the point of the stylus. The mode of operation is simple: The cylinder is revolved, and a sound thrown into the mouthpiece causes the iron disk, or dia

phragm, to vibrate, or tremble. This agitation is carried through the stylus to the tinfoil, and written upon it in irregular marks, dots and figures. When the utterance is to be reproduced the instrument is stopped, the stylus lifted from the groove, and the cylinder revolved backwards to the place of starting. The stylus is returned to its place. and the cylinder set to revolving forward. As the stylus plays up and down in the indentations, lines and figure: in the tinfoil, a quiver exactly equivalent to that produced by the utterance in the mouthpiece is communicated backwards to the diaphragm and thrown into the air. This agitation, being the equivalent of the original sound, reproduces that sound as perfectly as the machinery of the instrument will permit. Thus the phonograph is made to talk, to sing, to cry, to utter any sound sufficiently powerful to produce a perceptible tremor in the mouthpiece and diaphragm of the instrument. The phonograph makes it possible to read by the ear instead of by the eye, and it is not beyond the range of probability that the book of the future will be written in phonographic plates.

Probably the most marked and valuable invention of the age is the ELECTRIC LIGHT. The introduction of this system of illumination marks an important epoch in the history of our country. The project of introducing the electric light was agitated for the first time about the beginning of the eighth decade of the century. The advantages of such lighting, could the same be attained, were as many as they were obvious. The light is so powerful as to render practicable many operations as easily by night as by day. The danger by fire from illuminating sources is almost wholly obviated by the new system. A given amount of illumination can be produced much more cheaply by electricity than by any means of gas-lighting or ordinary combustion.

Early in 1875 the philosopher Gramme, of Paris, succeeded in lighting his laboratory by means of electricity. Soon afterwards the foundry of Ducommun and Company, of Mulhouse, was similarly lighted. In the following year the apparatus for lighting by means of carbon candles was introduced in many of the factories of France and other countries of Europe.

Lighting by electricity is accomplished in several ways. In general, however, the principle by which the result is effected is one, and depends upon the resistance which the electrical current meets in its transmission through various substances. There are no perfect conductors of electricity. In proportion as the non-conductive quality is prevalent in a substance, especially in a metal, the resistance to the passage of electricity is pronounced, and the consequent disturbance among the molecular particles of the substance is great. Whenever such resistance is encountered in a circuit, the electricity is converted into heat, and when the resistance is great, the heat is, in turn, converted into light, or rather the heat becomes phenomenal in light; that is, the substance which offers the resistance glows with the transformed energy of the impeded current. Upon this simple principle all the apparatus for the production of the electric light is produced.

Among the metallic substances, the one best adapted by its low conductivity to such resistance and transformation of force is platinum. The high degree of heat necessary to fuse this metal adds to its usefulness and availability for the purpose indicated. When an electrical current is forced along a platinum wire too small to transmit the entire volume, it becomes at once heated-first to a red, and then to a white glow-and is thus made to send forth a radiance like that of the sun. Of the non-metallic elements which offer similar resistance, the best is carbon. The infusibility