162 Tonson’s Ed. of 1758. Bacon may have had this passage in mind when he wrote, “It must not be thought that heat generates motion, or motion heat (though in some respects this be true), but that the very essence of heat, or the substantial self of heat, is motion and nothing else.”—_Novum Organum_, book ii. Devey’s Translation. 163 Doubtless, _at the sides_ of glacier beds, the range of temperature is greater. But there is evidence that the winter cold does not penetrate to the innermost recesses of glacier-beds in the fact that streams continue to flow underneath the ice all the year round, winter as well as summer, in the Alps and (I was informed in Greenland) in Greenland. Experimental proof can be readily obtained that even in midsummer the bottom temperature is close to 32° Faht. 164 Professor Tyndall “On the Conformation of the Alps,” _Phil. Mag._, Sept. 1862. 165 This had been crossed, for the first time, a few months before. 166 The following details may interest mountain-climbers. Left Zinal (5505 feet) 2.5 A.M. Thence to plateau S.E. of summit of Grand Cornier, 5 h. 25 min. From the plateau to the summit of the mountain, 2½ hours. The last 300 feet of the ridge followed were exceedingly sharp and narrow, with a great cornice, from which huge icicles depended. We were obliged to go _underneath_ the cornice, and to cut a way through the icicles. Descent from summit to plateau, 1 h. 40 min. Sharp snow-storm, with thunder. Plateau to summit of Col du Grand Cornier (rocks easy), 45 min. From the summit of the Col to the end of glacier leading to the west, 55 min. Thence to Abricolla (7959), 15 min. 167 The brother of my guide Michel Croz. 168 See note to p. 70. 169 See map of the Valley of Zermatt. 170 Couloirs are invariably protected at their bases by bergschrunds. An example of a couloir with a double bergschrund is given on p. 169. 171 The summit of the Dent Blanche is a ridge, perhaps one hundred yards in length. The highest point is usually at its north-eastern end. Several ascents besides those made by Mr. Kennedy and the author have been made in late years; but, as yet, no one seems to have discovered an easy route up the mountain. 172 The ascent of the Dent Blanche is the hardest that I have made. There was nothing upon it so difficult as the last 500 feet of the Pointe des Ecrins; but, on the other hand, there was hardly a step upon it which was positively easy. The whole of the face required actual climbing. There was, probably, very little difference in difficulty between the route we took in 1865, and that followed by Mr. Kennedy in 1862. 173 See Map of the Valley of Zermatt. The route taken upon June 19 is alone marked. 174 See Chap. III. pp. 44-5.