by Dan Wiswell
As we all know, many years ago there was a time when there were no electrical testing instruments. I often think of how difficult it must have been for the pioneers of the electrical industry to perform their experiments without even the most basic kinds of instrumentation. It must have been like finding your way in a dark room. Just like blacksmiths, they had to create their own tools. They did so to solve age-old mysteries that we now take for granted. Imagine living in a time when Volta invented the battery, Ampere had just defined our understanding of electrical currents, and Georg Ohm saw how it all fit together.
Remember, these events all took place at a time when there was no electrical infrastructure anywhere on the planet. The electrification of the world was still decades away. When the Leyden jar was invented in 1745 it became international news. We’ve all heard the stories of Benjamin Franklin and his kite with a key attached to its string. Ben Franklin’s experiment allegedly occurred seven years after the Leyden jar showed up. As a young person, what that story said to me was that back then, there must have been a lot of those kinds of experiments going on. The contributions of each philosopher-turned-scientist caused others to advance their own work. Hans Orsted’s experiments with magnetism brought the concept of the solenoid into the mind of Andre-Marie Ampere, which set the stage for the introduction of the telegraph. The first commercial telegraph was the Cooke and Wheatstone telegraph invented in 1837. The following year, the Morse system was invented by Samuel Morse. The Morse system eventually became the standard for international communication.
Very few things in the history of science have focused the attentions of so many people as did the telegraph. Bringing the telegraph from the laboratory into everyday use created an entirely new industry, which required a new set of skills from all the contributors that turned it into a reality. New hardware needed to be developed to manufacture a practical and easy to use utility. Insulators and wire mounting hardware evolved as the distribution system grew. Wire manufacturing companies struggled to meet the needs of this newly deployed creation. Instruments were designed to aid in the manufacturing and after-market servicing of this new field called telegraphy. An entire host of electrical instruments, called bridges, were developed and named by and for their creators. Names like Thompson, Wheatstone, Kelvin, Varley, and Kohlrausch all became attached to the devices that they created. Most of them were designed for measuring wire resistance and for finding faults in electrical circuits. All of them relied upon a singular device to make them work. That device was called the galvanometer.
The galvanometer can be considered as the Archaeopteryx of modern display technology. It was the first instrument designed to measure small amounts of electrical current. By unifying electricity, magnetism, and optics, the creation of devices like the mirror galvanometer became possible. The first device designed for this purpose was invented by Johann Christian Poggendorff in 1826. In 1858, an improved version of the mirror galvanometer was invented by William Thomson, who became Lord Kelvin in his later years. An example of Thomson’s mirror galvanometer is depicted on the previous page.
Thomson designed his galvanometer to test the first successful trans-Atlantic telegraph cable that was laid down in 1858. The previous year there was a failed attempt at bridging the Atlantic with a submerged telegraph cable, and Thomson had been involved with that project. When that failed attempt occurred, Thomson immediately set out to develop an instrument that was sensitive enough to detect the weak signals of the testing apparatus used during the testing of the cable.
Before we move forward, just stop and think for a moment. If the Morse telegraphic system was invented in 1838, it was only twenty years later that we successfully spanned the Atlantic with an electrical communication network. This foundational work paved the way for the construction of our electrical power infrastructure that began to develop in the 1880s. By the time the various Edison companies began supplying power to customers, we already had an understanding of the things that can go wrong with a distributed electrical system. As the telegraphic system was created to rely on battery power, it makes perfect sense that the original Edison concept of an electrical power circuit was based on a direct current system. This must have given weight to his argument and case against the use of the alternating current system that Westinghouse was advocating. The fact that our electric grid runs on AC power proves that no one, not even Thomas Edison, can stand in the way of progress for very long.
From the very beginning of electrical testing, it was discovered that the more sensitive the galvanometer used in creating a bridge circuit, the more accurate the test results would be when locating electrical faults. Mirror galvanometers were extremely sensitive by design. In them, a beam of focused light is deflected by its mirror and projected onto a scale. This had the effect of creating a long, mass-less pointer. The longer the beam, the greater the amplified signal. The Thomson mirror galvanometer was capable of detecting extremely small electrical testing signals in submerged trans-Atlantic telegraph cables.
Prior to the advent of more sophisticated testing instruments, telegraph systems were tested with batteries, galvanometers, and resistance coils. People tend to design new things based on, or to replace something that they are familiar with—take the horseless carriage for example. That is why the first portable DC power supplies were called “battery eliminators.” These devices helped define the values of voltage, current, and resistance in an electrical circuit. The instrument depicted below is an example of a resistance coil box that was used in those days in conjunction with batteries and galvanometers.
Advances in the understanding of electrical circuits that were defined with the aid of galvanometers began to take hold in other areas of study within the scientific community. Many of these occurred in the field of medicine. The first electrocardiogram was recorded in 1887 using what was called an electrometer. However, the first truly quantifiable test results in this field were obtained by what came to be known as a string galvanometer. In fact, the first courses in electricity that universities offered to students were part of the medical curriculum. This was due to the experiments of Luigi Galvani with static electricity, and the way in which he observed that it caused frog legs to react when stimulated by an electric current. It’s not surprising that the first galvanometers were named after Luigi Galvani and his experiments. Pictured below is another early example of a mirror galvanometer designed for laboratory use.
This Leeds and Northrup mirror galvanometer has an old-style, open-architectural design that allows us to see its components. In the picture on the right, notice the horseshoe magnet that is bridged by the meter movement. Light from the bulb at the bottom of the picture is focused through a lens and reflected off the mirror of the movement before it is redirected onto the reticle on the viewing glass in front of the instrument. These galvanometers have always reminded me of Isaac Newton’s reflecting telescopes.
Another significant advance in galvanometric design occurred with the merging of its basic concept and that of the d’Arsonval/Weston meter movement in the late 1880s (pictured below).
When this occurred, low-cost, high-quality galvanometers became available to the general public and quickly became ubiquitous in the front-panel designs of electrical measuring instruments manufactured by companies around the world. Pictured on this page are a few examples of portable instruments manufactured with galvanometers as an integral part of their front panel designs.
I believe that this was about the time at which electrical and electronic test equipment began to enter the modern era. Before this time, instruments were generally designed to act as building blocks that replicated the three legs of Ohm’s Law and its foundational parameters. Galvanometers could be scaled to measure current. With a known current deflection, resistors could be added in series to create volt meters or added in parallel to create higher current ammeters. Batteries supplied the circuit with a VA source.
Prior to the design of the d’Arsonval/Weston based movements, galvanometers were typically stand-alone devices that were paired with other stand-alone components to create the bridge circuits they were used in. These new, smaller galvanometers allowed for the creation of portable test equipment and elegantly designed laboratory standards that could resolve measurements with accuracies previously unachievable outside of a laboratory environment.
As the need for electrical measurement began to diversify, so did the design variations of galvanometers for specific applications. Today, these electro-mechanical indicators have become almost universally obsolete. Now, it is much more common to see instruments with graphical displays sporting apps that emulate these instruments that were created in the days of old. It is probably a natural tendency to think of these old instruments by comparing them to their modern equivalents, but I wonder. As Lord Kelvin was standing in a darkened laboratory observing the projected beam of light radiating from his galvanometer as it danced to the cadence of Morse code, did he envision an alternate future? What if his galvanometer had never been considered by d’Arsonval? What would have happened if he had colluded with the likes of Orsted and Maxwell? Maybe they would have created a movement with a mirror suspended in a manipulated magnetic field which could project those holographic images we see in science fiction movies. I remain hopeful and enthusiastic that one day I will see such things pass through my laboratory.
About the Author
Dan Wiswell is a self-described Philosopher of Metrology. He is president/CEO of Cal-Tek Company, Inc. and Amblyonix Industrial Instrument Company.
