What are the social consequences when science allows us to see things that had previously been invisible?

Scientists have revealed microscopic life, nanoscale molecules and galaxies billions of light-years away. These images have revolutionized the disciplines in which they were made, but they also transformed the public's imagination, giving common people new things to think and dream about.

The intertwined social, scientific and artistic impacts of 19th century photography is the subject of a new exhibit, Brought to Light Photography and the Invisible, 1840-1900, at San Francisco's Museum of Modern Art.

This gallery looks at some of the more astounding images and stories from the exhibit.

Left:
Hermann Schnauss, Electrograph of a brass wire gauge, 1900 As the men of industry attempted to harness electricity for profit, the public — which knew electricity primarily as lightning — had to be persuaded that this powerful, invisible force was something to invite into their homes. Electrographs like this one, produced by exposing a photographic negative with electricity, helped the public visualize and understand the mysterious electromagnetic waves that scientists were discovered populating the air.

"This is a moment where [scientists] are trying to harness electricity for practical purposes, but the general public was kind of skeptical," said Corey Keller, curator of the Brought to Light exhibit. "Their experiences with electricity were generally through lighting, which they knew could burn things down and kill you, if you weren't careful. So a great deal of time and money was spent trying to make electricity understandable and approachable."

In the early history of photography, capturing motion was out of the question. The photographic negatives of the time were not sensitive enough to light to be exposed over the short time periods required to capture fast action.

"If you look at 19th century cityscapes, you would think that Armageddon had taken place. You don't see any people," Keller said. "It's not that they aren't there, it's just that they don't show up because they walked through too quickly."

But by the end of the 1870s, more sensitive negatives brought motion within reach. Edward Muybridge was one of the first photographers to take advantage of the new abilities.

In this photo, we see one of Muybridge's motion studies: two men boxing in jock straps. Historians note that despite the scientific trappings, Muybridge's work was just art; it did not produce good scientific evidence about bodies' movements.

The ability to capture motion in photography opened up a previously invisible source of scientific data. Etienne-Jules Marey was a scientist trying to understand biomechanics, or the motion of the body, and he used photography to acquire information he couldn't get any other way, as in this photograph of a man on a stationary bicycle.

"What happens in this picture is that each split second exposure is layered on top of each other, so you get the sense of the full arc of the motion," Keller said. "And he's put a piece of tape down the arm and torso and the leg where the joints articulated, so as the leg went around and around the whole pedal stroke is outlined."

This wasn't just to create beautiful pictures; Marey was on a committee in France to improve the ergonomics of the newly popular bicycle.

"So by studying the motion of the leg, he would have been able to improve the engineering of the bicycle," Keller concluded.

While forward-looking scientists like Marey were using photography to understand, for example, how animals moved, as in this photo, others were less enthused about this new technology.

In particular, photographers' ability to capture images beyond what the human eye could perceive called into question an important tenet of 19th century science.

"What's amazing is that this is a moment where empirical observation in science is the most important thing, that idea of objective observation. And this kind of photography proved how completely useless a human observer was," said Keller. "So you end up with this photographic data that cant' be corroborated in any other way. It exists independently of any kind of perceptual experience."

Technology's ability to capture detail and motion more accurately than our eyes has only accelerated, of course, as anyone who has seen incredible ultra-slow-motion YouTube videos can attest.

When William Roentgen announced his discovery of X-rays, a photo of his wife's hand accompanied his paper as it made its way into the scientific community.

Over the next few years, images like this one of a skeletal hand with the ring came to symbolize X-rays. Practically, the hand is relatively flat and therefore easy to X-ray, but it was the aesthetics and grim-reaper symbolism that Keller said hit a nerve with the upper classes.

"It became fashionable to have an X-ray portrait taken of your hand," she said, calling attention to x-ray hand portraits of the last tsar of Russia and his wife.

The discovery of X-rays also touched off a lower-brow commercial craze. Within three months, DIY X-ray kits were available on the market. Photographers, who had access to most of the tools needed to make the images, began to train this new form of light on just about anything that might be beautiful.

"They were X-raying everything just to see what it looked like," Keller said.

One stunning example is this X-ray of a foot in a shoe from 1897. In fact, the connection between X-rays and extremities has remained strong. Even into the 1960s, shoe stores kept X-ray machines in their lobbies, both as marketing tools and to help their salesmen fit their patrons' feet correctly.

Throughout the second-half of the 19th century, photographers strived to unite the camera with the telescope. The moon, in particular, held a lasting fascination for astronomers and artists alike.

Imaging the moon, after all, was an immensely difficult task. The Earth rotates and the moon is actually a relatively faint object. It wasn't until John Adams Whipple and George Phillips Bond figured out how to rotate their camera ever so slightly to cancel out Earth's movement that simple images of our only satellite became possible.

What's interesting is that despite the fascination with creating pictures of the moon, like this striking image created in Spain, the images didn't add much for science beyond what detailed drawings could already do.

If you wanted close-up photos of the moon any time before the Apollo missions, you were pretty much out of luck. Unless, of course, you built incredibly detailed plaster models of lunar craters and then snapped carefully lit pictures of them. And that's exactly what an engineer and astronomer did in 1874 to tremendous acclaim.

James Nasmyth, the inventor of the steam hammer, and James Carpenter, then at the Royal Observatory in Greenwich, England, released a hugely successful book, The Moon: Considered as a Planet, a World, and a Satellite, illustrated by their incredible moon mock-ups. The august journal Nature gave the book a rapturous review.

"No more truthful or striking representations of natural objects than those here presented have ever been laid before his readers by any student of Science," the reviewer wrote.

But what's really appealing about the images isn't their "truthfulness" but their "truthiness."

"Astronomers were perfectly aware of what they were looking at," Keller said. "But they felt that because they were photographed, it added a layer of authenticity to the undertaking that simple drawings didn't have."

At the other end of the scale of size from the moon, other photographers were pushing their discipline into the microscopic realm. They had to devise new emulsion chemistries and types of equipment to capture clear images of tiny things.

Leading the charge was Auguste-Adolphe Bertsch, who worked to overcome any challenge that scientists threw at him. Unfortunately, he died during social unrest in France in 1871, and his images lay in a photographic archive until Keller brought them to the US for the exhibition.

Even as they solved technical challenges, the photomicrographers faced social resistance. The idea of representing a specific living thing instead of a generalized abstraction of an organism forced scientists to let go of long-held notions about their discipline.

"Prior to the 19th century, the scientific illustrations tend to represent a type, an ideal. So if you were going to do a picture of a flower, for example, the illustrator would look at 20 flowers and then take the common features and make an ideal flower," said Keller. "So, if that particular one happens to have a defective petal or something peculiar to it, you never really know: Does that photograph substitute then for that type of flower in general, or does it only represent that one specimen?"

While it may have posed a challenge for scientists of the 19th century, it's the unique nature of each photograph taken during this early period that wows us, even now.