Boys' Second Book of Inventions

by Ray Stannard Baker

Mr. Hewitt has found that the rays of his new lamp have a peculiar and stimulating effect on plant growth. A series of experiments, in which seeds of various plants were sown under exactly the same conditions, one set being exposed to daylight and one to the mercury gaslight, showed that the latter grew much more rapidly and luxuriantly. Without doubt, also, these new rays will have value in the curing of certain kinds of disease.

Further experimentation with the mercury arc led to the other two inventions, the converter and the interrupter. And first of the converter:

Hewitt's Electrical Converter.—The converter is simplicity itself. Here are two kinds of electrical currents—the alternating and the direct. Science has found it much cheaper and easier to produce and transmit the alternating current than the direct current. Unfortunately, however, only the direct currents are used for such practical purposes as driving an electric car or automobile, or running an elevator, or operating machine tools or the presses in a printing-office, and they are preferable for electric lighting. The power of Niagara Falls is changed into an alternating current which can be sent at high pressure (high voltage) over the wires for long distances, but before it can be used it must, for some purposes, be converted into a direct current. The apparatus now in use is cumbersome, expensive, and wasteful.

Mr. Hewitt's new converter is a mere bulb of glass or of steel, which a man can hold in his hand. The inventor found that the mercury bulb, when connected with wires carrying an alternating current, had the curious and wonderful property of permitting the passage of the positive half of the alternating wave when the current has started and maintained in that direction, and of suppressing the other half; in other words, of changing an alternating current into a direct current. In this process there was a loss, the same for currents of all potentials, of only 14 volts. A three-pound Hewitt converter will do the work of a seven-hundred-pound apparatus of the old type; it will cost dollars where the other costs hundreds; and it will save a large proportion of the electricity wasted in the old process. By this simple device, therefore, Mr. Hewitt has in a moment extended the entire range of electrical development. As alternating currents can be carried longer distances by using high pressure, and the pressure or voltage can be changed by the use of a simple transformer and then changed into a direct current by the converter at any convenient point along the line, therefore more waterfalls can be utilised, more of the power of coal can be utilised, more electricity saved after it is generated, rendering the operating of all industries requiring power so much cheaper. Every electric railroad, every lighting plant, every factory using electricity, is intimately concerned in Mr. Hewitt's device, for it will cheapen their power and thereby cheapen their products to you and to me.

Hewitt's Electrical Interrupter.—The third invention is in some respects the most wonderful of the three. Technically, it is called an electric interrupter or valve. "If a long list of present-day desiderata were drawn up," says the Electrical World and Engineer, "it would perhaps contain no item of more immediate importance than an interrupter which shall be ... inexpensive and simple of application." This is the view of science; and therefore this device is one upon which a great many inventors, including Mr. Marconi, have recently been working; and Mr. Hewitt has been fortunate in producing the much-needed successful apparatus.

The chief demand for an interrupter has come from the scores of experimenters who are working with wireless telegraphy. In 1894 Mr. Marconi began communicating through space without wires, and it may be said that wireless telegraphy has ever since been the world's imminent invention. Who has not read with profound interest the news of Mr. Marconi's success, the gradual increases of his distances? Who has not sympathised with his effort to perfect his devices, to produce a tuning apparatus by means of which messages flying through space could be kept secret? And here at last has come the invention which science most needed to complete and vitalise Marconi's work. By means of Mr. Hewitt's interrupter, the simplicity of which is as astonishing as its efficiency, the whole problem has been suddenly and easily solved.

Mr. Hewitt's new interrupter may, indeed, be called the enacting clause of wireless telegraphy. By its use the transmission of powerful and persistent electrical waves is reduced to scientific accuracy. The apparatus is not only cheap, light, and simple, but it is also a great saver of electrical power.

The interrupter, also, is a simple device. As I have already shown, the mercury vapour opposes a high resistance to the passage of electricity until the current reaches a certain high potential, when it gives way suddenly, allowing a current of low potential to pass through. This property can be applied in breaking a high potential current, such as is used in wireless telegraphy, so that the waves set up are exactly the proper lengths, always accurate, always the same, for sending messages through space. By the present method an ordinary arc or spark gap—that is, a spark passing between two brass balls—is employed in sending messages across the Atlantic. Marconi uses a spark as large as a man's wrist, and the noise of its passage is so deafening that the operators are compelled to wear cotton in their ears, and often they must shield their eyes from the blinding brilliancy of the discharges. Moreover, this open-air arc is subject to variations, to great losses of current, the brass balls become eroded, and the accuracy of the transmission is much impaired. All this is obviated by the cheap, simple, noiseless, sparkless mercury bulb.

"What I have done," said Mr. Hewitt, "is to perfect a device by means of which messages can be sent rapidly and without the loss of current occasioned by the spark gap. In wireless telegraphy the trouble has been that it was difficult to keep the sending and the receiving instruments attuned. By the use of my interrupter this can be accomplished."

And the possibilities of the mercury tube—indeed, of incandescent gas tubes in general—have by no means been exhausted. A new door has been opened to investigators, and no one knows what science will find in the treasure-house—perhaps new and more wonderful inventions, perhaps the very secret of electricity itself. Mr. Hewitt is still busily engaged in experimenting along these lines, both in the realm of abstract science and in that of practical invention. He is too careful a scientist, however, to speak much of the future, but those who are most familiar with his methods of work predict that the three inventions he has already announced are only forerunners of many other discoveries.