Wind has mass and flows very similarly to water, swirling around objects, rising over objects or terrain, forming eddies etc. We see it clearly as water flows, but can't see wind, only the effects. Watching wind on lake water is probably the best visual evidence of just how it flows. You can actually see wind currents, eddies, dead spots, even see a gust approaching on the surface of water. And of course, we've all seen that wind effect on water that looks like a dorsal fin moving along just under the surface!