THE four of us were trekking through the Chashme Iskandar area, a wild region in the Zagros Mountains of Iran. We were all soft-shoe rock climbers, and our objective was to scout out a southern route to the Kuh-i-Hazar, a magnificent mountain that reared its 14,700-foot snow-covered peak several miles to the north. I don’t know exactly how to describe it, but, in the presence of such a marvel, you get the same feeling of reverence as in a great cathedral.The others were all young geologists, determined to unlock the secrets of the intense folding of the Zagros, while I was a physicist, some years older than the rest, conscripted in order to provide scientific respectability to the expedition. My own particular passion at the time was climatology, so I always carried with me the tools of the trade: various thermometers, a sling psychrometer for measuring relative humidity, and an aneroid barometer.It wasn’t particularly high here, around 4,000 feet, high enough to provide some relief from the baking 120-degree heat of the desert below us. Nevertheless, in the bone-dry air, our canteens were empty by midday, and coming to a mountain torrent, we decided to cross over before refilling them. The water was the milky turquoise of glacier melt, and, with the snowcap towering above us, we had no doubt that getting across was going to be a cold business.Accordingly, we stripped off and, holding our belongings over our heads, threaded our way gingerly over the sharp stones of the streambed. The ice-cold water was only waist deep, but by the time we got to the other side our teeth were chattering, our skin was blue with cold and we had to light a fire to get some warmth back into our bones. It was while I was rubbing my feet to restore circulation that it suddenly occurred to me that something was wrong.Although the nearest glacier was only a few miles to our north, the stream had to cross several intervening ridges and, since these all ran east-west without a break for several miles, it must have traveled at the very least 20 miles before reaching us.And if that was true, the water temperature could hardly be much lower than the local ambient of 105 degrees Fahrenheit. So I unshipped a couple of thermometers from my pack and stuck them in the stream. Sure enough, they both registered 100 degrees, slightly higher than body temperature.Armed with this new knowledge, I waded back into the water and this time found it pleasantly warm. Evidently, minute particles of clay suspended in the water, coupled with the glistening snow above us and the sharp stones of the streambed to distract our critical faculties, had combined to override the evidence of our senses, and we felt like a bunch of idiots to be so easily taken in by deceitful Mother Nature.But we all have our pride, and I sensed that the others were none too thrilled that I had exposed their credulity with my thermometers.