1. The thermometer was not a single invention, rather, an instrument developed and improved over time by multiple inventors. Various authors have credited the invention of the thermometer to Cornelis Drebbel, Robert Fludd, Galileo Galilei or Santorio Santorio. Each inventor and each thermometer was unique because there was no standard scale. In 1665 Christiaan Huygens suggested using the melting and boiling points of water as standards, and in 1694 Carlo Renaldini proposed using them as fixed points on a universal scale. In 1701 Isaac Newton proposed a scale of 12 degrees between the melting point of ice and body temperature. Finally in 1724 Daniel Gabriel Fahrenheit produced a temperature scale which now (slightly adjusted) bears his name. In 1742 Anders Celsius proposed a scale with zero at the boiling point and 100 degrees at the freezing point of water, though the scale which now bears his name, has them the other way around. Sources: Brannan Wikipedia
2. Georg Simon Ohm, (born March 16, 1789, Erlangen, Bavaria [Germany]—died July 6, 1854, Munich), German physicist who discovered the law, named after him, which states that the current flow through a conductor is directly proportional to the potential difference (voltage) and inversely proportional to the resistance. Source: Brittanica
3. The first transistor. This doesn’t look like it would change the world, but this first transistor did just that. This replica is a bit larger than the original, but otherwise a pretty faithful representation. In 1947 Walter Brattain at Bell Labs fashioned it out of plastic stand, a chunk of germanium, a triangular piece of plastic with a layer of gold on each side, and a “spring” on top to press the gold at the apex of the triangle into the germanium – that’s why its called a “point contact” transistor. Here’s what Bardeen and Brattain actually did with this device on December 23, 1947. They hooked up a microphone to the left side, and an oscilloscope to the right side. As they spoke into the microphone they could see the voice signal being amplified. As Brattain wrote in his lab notebook “This circuit was actually spoken over and by switching the device in and out a distinct gain in speech level could be hear and seen on the scope ….” Source: EngineerGuy.com
4. Joseph Priestley’s “The Nature and Properties of Gases.” Priestley’s first scientific work, The History of Electricity (1767), was encouraged by Benjamin Franklin, whom he had met in London. In the 1770s he began his most famous scientific research on the nature and properties of gases. At that time he was living next to a brewery, which provided him an ample supply of carbon dioxide. His first chemical publication was a description of how to carbonate water, in imitation of some naturally occurring bubbly mineral waters. Inspired by Stephen Hales’s Vegetable Staticks (first edition, 1727), which described the pneumatic trough for gathering gases over water, Priestley began examining all the “airs” that might be released from different substances. Many, following Aristotle’s teachings, still believed there was only one “air.” By clever design of apparatus and careful manipulation, Priestley isolated and characterized eight gases, including oxygen — a record not equaled before or since. In addition, he contributed to the understanding of photosynthesis and respiration. Source: chemheritage.com
5.The electromechanical relay, used as a constructive part of some early calculators and computers (see computers of Zuse, Aiken and Stibitz), was invented in 1835 by the brilliant US scientist Joseph Henry (1797–1878), known mainly as the inventor of the electromagnetic phenomenon of self-inductance and mutual inductance (see the nearby photo for Henry’s electromagnet from 1831). Henry was only really interested in the science of electricity and the relay was a laboratory trick to entertain students.
Samuel Morse later used Henry’s relay device to carry morse-code signals over long kilometers of wire, but generally the invention of Henry remained relatively unknown for several decades, but in 1860s, and later on in the end of 19th century, with the development of telegraph and phone communications, it became widespread. Especially after invention of the rotary dial, first developed in USA by Almon Strowger in 1890, which however used not the simple two-position switches described bellow, but ten-position relays, the phone companies became a huge consumer of electromechanical relays. Read more. Source: History of Computers