Overview:
This book, “The Telephone,” published in 1877 by Prof. A. E. Dolbear, provides a comprehensive account of the science behind the telephone and offers detailed instructions for constructing one. Dolbear begins by outlining the historical development of electricity, magnetism, and sound, explaining each phenomenon through clear examples and illustrations. He then examines the various technologies that were used to generate electricity, including thermo-electricity, magneto-electricity, and secondary currents, highlighting the crucial role of magnetic induction in the telephone.
The book then dives into the nature of sound, discussing its propagation, the composition of sound waves, and the concept of pitch. Dolbear explores the science behind timbre, explaining how overtones contribute to the unique quality of different musical instruments and voices. He also describes the work of Helmholtz, who dissected and synthesized sounds to understand their underlying structure and discovered the mechanisms by which different instruments and voices produce their distinctive tones. The book culminates with a detailed explanation of Dolbear’s own invention of the speaking-telephone, highlighting the key breakthroughs in the technology and providing specific instructions for building a working model.
Key Findings:
- The telephone, as invented by Dolbear and Bell, was not simply transmitting sound over a wire but rather converting energy between forms: sound to electricity to magnetism to sound.
- Understanding the science behind electricity, magnetism, and sound was crucial for developing a working telephone.
- The telephone was still in its infancy in 1877, with potential for future improvements and applications.
Learning:
- Electricity: Learn about the various methods of generating electricity, including friction, chemical action, thermo-electricity, and magneto-electricity. Discover that static and dynamic electricity are not fundamentally different, but rather variations in how electricity is generated and stored.
- Magnetism: Explore how magnets are created and understand the concept of magnetic induction. Learn how magnetism can be induced in iron and steel through the application of electric currents.
- Sound: Understand how sound waves are created and travel through the air, and how pitch is determined by the frequency of vibrations. Gain insights into timbre, the unique quality of sound, and how it is determined by the presence of overtones.
Historical Context:
The book was published in 1877, a time of intense interest and rapid development in the field of telephony. The telephone had just been invented, and Dolbear’s book reflects the excitement and curiosity surrounding this groundbreaking technology. The book also showcases the scientific advancements of the preceding century, particularly in the fields of electricity and magnetism, which paved the way for the invention of the telephone.
Facts:
- Magnetite: A magnetic iron ore, containing 72.5% iron.
- Hematite: An iron ore containing 70% iron, but not magnetic.
- Magneto-electric Machines: Generate electricity through the motion of coils of wire in front of permanent magnets.
- Induction Coils: Produce high-voltage secondary currents through the interaction of two coils, one of which is connected to a battery.
- Lightning: A form of static electricity, with a striking distance determined by the amount of charge.
- Magnetism: Not a substance, but a form of motion in the ether, affecting ordinary matter through attractions and repulsions.
- Sound Velocity: Travels at 1,093 feet per second in air at freezing point, and increases with temperature.
- Octave: A musical interval representing a doubling or halving of the frequency of vibrations.
- Overtones: Harmonics or upper partial tones that accompany the fundamental tone in a musical sound, contributing to its timbre.
- Timbre: The unique quality of a sound, determined by the number and intensity of overtones.
- Resonance: The amplification of sound when a vibrating object is placed on a larger, resonant surface.
- Organ Pipes: Produce sound through the vibration of a column of air inside the pipe, and their timbre is influenced by their shape and size.
- Violin: A challenging instrument to master, with a complex timbre due to the numerous overtones it can produce.
- Human Voice: Rich in overtones and highly individual, making it impossible to tabulate the components of its timbre.
- Intermittent Current: A current that is repeatedly broken and restored, producing clicks when passed through an electromagnet.
- Helmholtz’ Electric Interrupter: A device that breaks a circuit in sync with the vibrations of a tuning fork, creating a sound of a specific pitch.
- Reiss’ Telephone: Used a vibrating membrane to interrupt an electric current, producing a sound with the same pitch as the source but lacking the complexity of speech.
- Gray’s Telephone: Utilized an induction coil and a rotating drum to create musical tones by varying the current.
- Bell’s Telephone: Employed a vibrating iron armature to induce electrical pulses in a circuit, enabling the transmission of speech.
- Dolbear’s Telephone: Used a thin steel plate vibrating in front of a powerful magnet to generate electrical pulsations, leading to the first successful speaking-telephone.
Statistics:
- Sir Isaac Newton’s Magnet: A 3-grain magnet could lift 750 grains (250 times its weight).
- Largest Known Magnet (M. Obelliane): Lifts 40 times its own weight.
- Yale College’s Electromagnet: Weighing 59 pounds, it could sustain 2,500 pounds (over 40 times its own weight).
- Dr. Joule’s Electromagnet: Supported 3,500 times its own weight (140 times the proportionate load of Newton’s magnet).
- Speed of Sound: 1,125 feet per second at 60° Fahrenheit.
- Standard Pitch (Concert A): 440 vibrations per second.
- Human Hearing Limits: Lower limit – 23 vibrations per second (some individuals may perceive lower frequencies). Upper limit – 38,000 vibrations per second (varies significantly between individuals).
- Induction Coil (Stevens Institute): 50 miles of secondary wire, producing a 21-inch spark.
- Largest Induction Coil (Spottiswood): 280 miles of secondary wire, generating a 42-inch spark.
- De La Rue’s Battery: 8,040 cells produced a spark 0.345 inches long.
Terms:
- Electricity: A fundamental force of nature, manifested as attractions and repulsions between charged particles.
- Magnetism: A force generated by magnetic materials, affecting other magnetic materials and electric currents.
- Electromagnetism: The interaction between electricity and magnetism, where electric currents create magnetic fields and magnetic fields can induce electric currents.
- Polarization: The buildup of unwanted chemical products on the electrodes of a battery cell, reducing its efficiency.
- Induction: The process of generating electricity in a coil of wire by changing the magnetic field near it.
- Resonance: The amplification of sound waves when a vibrating object is placed on a surface that can vibrate at the same frequency.
- Timbre: The unique quality of a sound, distinct from its pitch, determined by the presence of overtones.
- Overtones: Harmonics or upper partial tones that accompany the fundamental tone, contributing to the timbre of a sound.
- Fundamental Tone: The lowest and usually strongest tone in a musical sound.
- Sympathetic Vibrations: The tendency of objects to vibrate at their resonant frequencies when exposed to sound waves of that frequency.
- Intermittent Current: A current that is repeatedly broken and restored, often used in telephone technologies.
Examples:
- Magnetic Cars: Used by the Chinese over 3,000 years ago to navigate vast steppes of Tartary.
- Fiddler’s Bridge: A musician caused a bridge to shake violently by playing a note that resonated with the bridge’s structure.
- Lovers’ Telegraph: A simple device using a taut string to transmit sound between two tin cans.
- Piano Sounding Board: A large, thin board that amplifies the vibrations of the piano strings, contributing to its overall sound.
- Tuning Fork and Bottle: A tuning fork will resonate with a bottle filled to a specific depth with water, demonstrating the relationship between sound frequency and the length of a resonant air column.
- Comb and Paper: A strip of paper placed in front of a vibrating comb will produce a sound, showing how membranes respond to vibrations.
- Opeidoscope: An instrument using a thin rubber membrane to visualize sound vibrations through the reflection of light.
- Helmholtz’ Electric Interrupter: A device used to maintain the vibrations of a tuning fork by repeatedly making and breaking an electric circuit in sync with the fork’s oscillations.
- Reiss’ Telephone: Used a vibrating membrane to interrupt an electric current, demonstrating the ability to transmit a basic sound signal over a wire.
- Gray’s Musical Telephone: Enabled the transmission of musical sounds by using electromagnets to vibrate reeds tuned to specific frequencies.
Conclusion:
Professor Dolbear’s “The Telephone” provides a captivating journey into the science behind this revolutionary invention. It showcases how a deep understanding of electricity, magnetism, and sound was crucial for its development and reveals the ingenious ways in which these forces can be manipulated and transformed. The book also highlights the ongoing potential for the telephone, suggesting that this groundbreaking technology was just beginning to reveal its true possibilities. The reader gains a comprehensive understanding of the scientific principles that underpin the telephone, as well as a glimpse into the historical context surrounding its invention.