Water Rushing Through Cities, The Gentle Version : Krulwich Wonders... Human beings are two-thirds water — and one could think of us forming a river as we move through life. Contemplating these striking photos from St. Petersburg, it's not so hard to believe.

Water Rushing Through Cities, The Gentle Version

Henry David Thoreau was looking into a pond one day — it was his local pond, Walden, in Concord, Massachusetts — and as he looked, a fish, a pickerel, slid into view. That fish was so comfortable, so at ease in the water, Thoreau wrote in his diary that its muscles, its fins, its scales were almost water in a different form, "animalized water," he called it. And 150 years later, the great science writer Loren Eiseley said the same thing about people.

We're two-thirds water, after all. Our cells carry, "a concentration of that indescribably and liquid brew which is compounded in varying proportions of salt and sun and time."

And so, like water, we flow. Or, let's try to imagine ourselves flowing. We may not realize it when we're in the flow, but take a look at these pictures from St. Petersburg. Russian photographer Alexey Titarenko sees city crowds as a stream of hands, heads and coats rushing along stairs and streets, in and out of buildings...rushing like water...

Eiseley, by the way, described people as, "those myriad little detached ponds with their own swarming corpuscular life, what [are] they but a way that water has of going about beyond the reach of rivers?"

And taking this metaphor one step further, when you peek in on water itself, the real stuff...yes, it's all around us, flowing, cascading; we drink it in and spit it from our mouths, but again, watch what happens when you slow it down, way, way down, as camera man Tom Guilmette did using a high speed digital camera. All of a sudden — (well in this case you have to wait a minute for Tom land on a bed, followed by dropping coins, but then — a minute in...watch out...) — water moving at a glacial pace gets all globular and bullet like and shimmery and...oh, I don't know. Just watch.

I've said this before and I'll say it again, quoting Eiseley: "If there's magic on this planet, it's contained in water."