Elisha Gray, best known for his patent dispute with Alexander Graham Bell over the telephone, wrote this volume as the third in his Nature's Miracles series. The book is explicitly aimed at a general audience, with Gray stating that technical terms are avoided or clearly explained. It is not an exhaustive treatise but a popular account that blends historical narrative, theoretical explanation, and practical description of electrical inventions.

The author's personal involvement in the development of telegraphy and telephony is evident throughout. Gray describes his own harmonic telegraph system, which he says successfully sent eight simultaneous messages between New York and Philadelphia in 1876-77. The excerpts show a writer who treats scientific principles as directly connected to everyday experience, even drawing a moral analogy between tuning and human sympathy.

A Practitioner's Perspective on Electrical Science

Gray introduces himself as someone who has spent thirty-five years studying electricity and inventing appliances for transmitting intelligence. This practical background shapes the book's approach. Unlike a purely theoretical text, Gray frequently refers to his own experiments and devices. The harmonic telegraph, which he invented, is described in detail with diagrams and operational principles.

The author's voice is that of an engineer explaining his craft. He describes how tuned reeds at the transmitting end correspond to matching reeds at the receiving end, each vibrating at a specific frequency. The system allowed multiple messages to travel simultaneously over a single wire because each frequency was independent. Gray notes that if sender and receiver are out of tune, no message can be sent—a principle he extends to a life lesson about harmony with one's surroundings.

The Way Duplex System and Practical Telegraphy

Chapter XIV presents the Way Duplex system, another invention by Gray that grew out of the harmonic method. This system allowed a railroad telegraph line to handle both through business between end offices and local station traffic simultaneously. Gray explains that each end of the line has a constantly vibrating tuned reed, and a harmonic relay tuned to match the sender's reed. When a key is depressed, the line current becomes vibratory, enabling selective reception.

The description is technical but accessible. Gray emphasizes that the system was still in use on some railroad lines at the time of writing. This chapter illustrates how Gray's inventions addressed real-world communication needs, particularly for train dispatching where multiple offices needed to share a single line efficiently.

Historical and Theoretical Foundations

The book's table of contents reveals a structured progression: after chapters on the history of electrical science and magnetism, Gray moves to theory, currents, generators, atmospheric electricity, and measurement. Later chapters cover telegraphy, telephony, submarine cables, and even wireless telegraphy. The final chapters discuss industrial applications like Niagara Falls power generation and electrical products such as carborundum, bleaching powder, aluminum, and calcium carbide.

Gray's treatment is deliberately broad. He aims to plant seed-thoughts that will awaken interest in natural science, especially electricity. The excerpts show that he avoids dense mathematics in favor of conceptual explanations. For example, he explains harmonic telegraphy by analogy to tuning forks and sympathetic vibration, a phenomenon many readers would have encountered with musical instruments.

Readers should approach this book as a historical document from a key inventor of the electrical age. Gray's personal involvement in the technologies he describes gives the text a unique authority, but his claims—such as sending eight simultaneous messages—should be considered in the context of late-19th-century telegraphy. The book is best read alongside other contemporary accounts to understand the competitive landscape of early electrical communication.