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Here at PopSci, there’s nothing we love more than figuring out how something works, be it the latest technology, or a scientific breakthrough. That moment of discovery – let’s call it a “how it works moment” – is almost as exciting for us buffs as it is for the researchers.

Here, we take a look back at some of history’s most fascinating “how it works moments” and the images that define them. It’s not always a cutaway or a teardown, but our desire to see how things work with our own eyes hasn’t changed over the years.

Click to launch a gallery of historical “how it works moments.”

Human Anatomy

In the early 16th century, much of doctors’ knowledge of the human body came from Galen, a physician from ancient Rome. Andreas Vesalius learned that in the Roman religion, the dissection of human bodies was forbidden, and that Galen’s version of human anatomy was likely speculation based on dissections of other animals. He began doing dissections on cadavers himself, studying the human body and eventually publishing a more accurate description of human anatomy than ever before, complete with illustrations, like the one seen here.


Copernicus’ discovery that the sun, not the Earth, was at the center of the universe was an incredibly controversial claim in the 16th century, especially with regard to religious beliefs that the Earth did not move. However, the geocentric model did not work with Aristotle’s claim that all celestial bodies have uniform circular motion. This resistance to heliocentrism may have contributed to the fact that Copernicus’ work On The Revolution Of Heavenly Spheres was not published until he was on his deathbed. Here we see Copernicus’ model of the solar system – with the sun at the center.

Smallpox Vaccine

Edward Jenner‘s “how it works moment” came when he realized that people who were exposed to cowpox, a disease found in cows that was fairly harmless, could not contract smallpox. To that point, the only method of vaccinating against smallpox involved giving the patient a mild case of the disease itself, which didn’t always stay mild and sometimes led to death. In 1796, using part of a cowpox lesion found on a young milkmaid, Jenner inoculated an 8-year-old boy, who became mildly ill, but recovered within 10 days. Several weeks later, he inoculated the boy with smallpox. He was right – the boy showed no signs of the disease. This image is a drawing of the cowpox lesions on the dairymaid’s hand. Smallpox vaccine later led to the complete eradication of the disease in the 1970s.

Discovery of Microorganisms

In the 17th century, Anton Von Leeuwenhoek made over 500 “microscopes,” some of which are illustrated here. They were not compound microscopes like we have today, rather very powerful magnifying glasses. Viewing a sample of lake water under one such microscope, he observed and described microorganisms present in the water, including algae. He went on to observe many other microorganisms.

Identification of Mitosis

Comparing living cells to stained slides allowed Walther Flemming to determine the stages of mitosis and their order. He used then-newly-discovered aniline dyes to identify a thread-like material in the nucleus of the observed cells, later determined to be chromosomes. This illustration shows cell divisions Flemming observed in the human cornea.

Role Of The Chromosome In Heredity

Thomas Hunt Morgan noticed a rare trait in one of his Drosophila fruit flies – white eyes. So he bred it with the other, red-eyed flies. The resulting generation had entirely red eyes, but interbreeding resulted in some white-eyed flies in the second generation, all of which were male. So he posited that the gene for this trait was found on the X chromosome and developed his theory of sex-linked characteristics. This illustration of his experiment was published in Popular Science in 1914.

The First Photograph

Using a method he called heliography, Nicephore Niépce created the world’s first photograph, seen here, in the early 19th century. Not good enough at drawing for lithography, he instead used a camera obscura and a pewter plate coated with a kind of asphalt that hardens in the light to permanently fix the image seen here, a view from his window.

Natural Selection

Perhaps the most famous example of figuring out how something works is Charles Darwin‘s theory of natural selection. His five year voyage aboard the HMS Beagle allowed him to study wildlife around the globe, which led to his landmark observations of variations of finches’ beaks (illustrated here) on the Galapagos Islands. Contrary to popular belief, though, Darwin did not have his “how it works moment” on the islands. It took many more years of work for him to develop his theory.

Continental Drift

Sometimes a “how it works moment” can come from just looking at ordinary things in a new way. Such was the case for Alfred Wegener, who noticed that the coastlines of Africa and South America fit together like pieces in a jigsaw puzzle. While he wasn’t the first to notice this, he began to piece the puzzle together, noticing that geographic features on different continents tended to correspond, such as the North American Appalachians and the Scottish Highlands. He used this evidence to develop his theory of continental drift. The theory stated that the continents had split off from a single land mass. This map from his The Movements of the Continents and the Oceans shows different stages of this process. After publication of his theory, much of the scientific community rejected it outright. It took several decades and research by many other scientists before his theory was finally accepted.

Discovery of Penicillin

In 1928, when his staphylococcus culture plate became infested with mold, Alexander Fleming noticed that the bacteria wasn’t growing around the mold, as shown in this image. Further experiments showed that the mold was effective against bacteria, even when diluted 800 percent. This compound, which came from the penicillium notatum mold, he named penicillin. He shares a Nobel Prize in Medicine with Howard Florey and Ernst Chain, two scientists who worked with penicillin during World War II.