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. The chief pursuit of science and invention in this day of wonders is the electrical conquest of the world, the introduction of the electrical age. The electric motor is driving out the steam locomotive, the electric light is superseding gas and kerosene, the waterfall must soon take the place of coal. But certain great problems stand like solid walls in the way of development, part of them problems of science, part of mechanical efficiency. The battle of science is, indeed, not unlike real war, charging its way over one battlement after another, until the very citadel of final secret is captured. Mr. Hewitt with his three inventions has led the way over some of the most serious present barriers in the progress of technical electricity, enabling the whole industry, in a hundred different phases of its progress, to go forward. THE END [Transcriber's Note: Obvious punctuation errors have been silently repaired. The oe-ligatures have been replaced by "oe". All words printed in small capitals have been converted to uppercase characters. Inconsistencies, for example in hyphenation and spelling, have been retained. Page 182: "Burnburg" is actually called "Bernburg".] End of the Project Gutenberg EBook of Boys' Second Book of Inventions, by Ray Stannard Baker