At six o'clock the sun was still shining beautifully, and we anxiously waited for the time when it would be low enough to raise our shadows to the misty wall. An hour afterwards, a hundred visitors were out, and many of us were on the "spectre" stones. There was great excitement in anticipation of the weird appearances, which had attracted us from such a distance. But, almost at the moment of success, the sun descended behind a belt of purple cloud, and all we saw was part of a rainbow on the misty hollow. For the sun never appeared again. This was intensely saddening, seeing that, but for that stratum of cloud above the horizon, the phenomenon would have been graphically displayed. The cold became suddenly intense, and we had to sleep with a freezing mist enveloping the hotel. In vain did we wait for the wakening call, to tell us of sunrise; for the sun could not pierce the mist, and we had to return home disappointed. Sometimes the rainbow colours assume the shapes of crosses instead of circles. Occasionally a bright halo will be seen above the shadow-head of the observer, concentric rainbows enclosing all. In some recorded cases the grand effect must have been simply glorious. Scientific observation has done much to dispel the superstition which has clung so tenaciously to the Highland mind. The lonely grandeur of the weird mountain giants has been clearly explained as perfectly natural, yet the awe-striking feeling cannot be entirely driven off. CHAPTER XXVIII THE WIND Once was the remark pointedly made: "The wind bloweth where it listeth." And that is nearly true still. The leading winds are under the calculation of the meteorologist, but the others will not be bound by laws. Yet there are instruments for measuring the velocity and force of the wind, after it is on; but "whence it comes" is a different matter. A gentle air moves at the rate of 7 miles an hour; a hurricane from 80 to 150 miles, pressing with 50 lbs. on the square foot exposed to its fury. Some of the gusts of the Tay Bridge storm, in 1879, had a velocity of 150 miles an hour, with a pressure of 80 to 90 lbs. to the square foot. Before steamers supplanted so many sailing vessels, seamen required to be always on the alert as to the direction and strength of the wind, and the likelihood of any sudden change; and they chronicled twelve different strengths from "faint air" to a "storm." In general, the wind may be considered to be the result of a change of pressure and temperature in the atmosphere at the same level. The air of a warmer region, being lighter, ascends, and gives place to a current of wind from a colder region. These two currents--the higher and the lower--will continue to blow until there is equilibrium.