Malia Wollen:

In 1861, the photographer Carleton E. Watkins hauled hundreds of pounds of camera equipment, sheets of glass and chemicals into Yosemite Valley in a darkroom wagon. For the first time, Mr. Watkins captured photographic images of these granite cliffs and waterfalls.

After seeing Mr. Watkins’s photographs, President Abraham Lincoln signed legislation in 1864 preserving the valley for the public and leading the way toward what would become the National Park Service.

In a strange coincidence, the molten effect of the sun on Horsetail Fall resembles another famous and highly photographed firefall here, one involving actual fire. Beginning around 1900, park workers collected Red Fir bark and built a large bonfire atop Glacier Point. After dark they pushed the red embers off the cliff in a cascade of glowing red coals, a must-see spectacle for the summer tourist set.

But in 1968, park officials ended the Yosemite Firefall, citing its man-made unnaturalness (the park banned feeding bears for the same reason). Five years later, the photographer and mountain climber Galen Rowell was driving through the park after a winter climb when he spotted the light catching in Horsetail Fall. He rushed across the valley and took what is believed to be the first image of the illuminated waterfall.

Mr. Rowell died in a plane crash in 2002, but his “Last Light on Horsetail Fall” remains the most well-known photograph of the apparition.

Douglas Rushkoff:

Facebook is just such a technology. It does things on our behalf when we’re not even there. It actively misrepresents us to our friends, and worse misrepresents those who have befriended us to still others. To enable this dysfunctional situation — I call it “digiphrenia” — would be at the very least hypocritical. But to participate on Facebook as an author, in a way specifically intended to draw out the “likes” and resulting vulnerability of others, is untenable.

Facebook has never been merely a social platform. Rather, it exploits our social interactions the way a Tupperware party does.

Facebook does not exist to help us make friends, but to turn our network of connections, brand preferences and activities over time — our “social graphs” — into money for others.

We Facebook users have been building a treasure lode of big data that government and corporate researchers have been mining to predict and influence what we buy and for whom we vote. We have been handing over to them vast quantities of information about ourselves and our friends, loved ones and acquaintances. With this information, Facebook and the “big data” research firms purchasing their data predict still more things about us — from our future product purchases or sexual orientation to our likelihood for civil disobedience or even terrorism.

The true end users of Facebook are the marketers who want to reach and influence us. They are Facebook’s paying customers; we are the product. And we are its workers. The countless hours that we — and the young, particularly — spend on our profiles are the unpaid labor on which Facebook justifies its stock valuation.