The one in which I had hoped to find the first trout of the year was invisible just above the cascade : ice-covered from bank to bank. However, it was still awake underneath; and I remembered that a mile farther up there was a long stretch of it nearly flat; the sun, at noontide now, would be striking full upon it there ; perhaps it would be open.

It was partly so. On all the long stretch there was no place at which the stream was free from bank to bank. Everywhere, from the sides, the shapeless ice protruded; the blue water in the middle was tearing past as if it were a living thing in fear of enemies on both flanks; but here and there the stream seemed to be holding its own in fighting the frost, and had actually a few yards in which to breathe.

I cast the flies into one of those open spaces; and cast again, again, and again. What was the matter ? Had I forgotten how to throw a fly ? The line was falling heavily, not with a splash exactly, but with an ungainly mark of its whole length on the swift water, notably the gut part of it, which should fall unseen ; at each successive cast the mark became larger; unless I was mistaken, the line was heavier than it should be. I reeled up, and looked to see what was wrong.

The cast was like a dainty string of pearls. Apparently it had in some magical manner threaded its way through hundreds of precious stones. There they were; fixed, smooth-crystal, dimly glistening in the sunbeams; and set upon the opaque line, from end to end, with a regularity which the deftest craft could not excel.

They were frozen drops of water. How had they been formed ? or, rather, where ?

Sorrowfully when the lake is unruffled by a breeze, or the stream is smooth, all of us know that, as has been mentioned, a cast of other than thin gut carries forward in its flight a shower ; but had these solid beads of water been formed when the line was in the air ? As they did not melt when bathed in the sunlight, I realised that the temperature must be low, and it was possible to think that the drops had been frozen in the air; but a subversive doubt beset me. Could it be that the beads, formed and fixed, had been snatched bodily from the stream itself ?

This thought was incompatible with the accepted understanding about water. Many a midnight, walking homeward from an hour or two of after-dinner billiards at the Club, my friend Rudolph Messel, whose scientific knowledge is honoured in London and Paris and Berlin, had entertained me with fascinating discourses on the phenomena of nature. One night, when the setting-in of frost was shown by the transfiguration of Piccadilly from muddy dinginess into a steely-gray sparkling under the electric glow, Dr. Messel had dwelt on the fact that water is the only fluid which expands in freezing. If it contracted, instead of expanding, all living creatures in the lakes and streams would, he had said, become extinct. The settling of the ice would begin at the bottom; and when the whole body of the water was frozen, as it would quickly be, practically remaining so through the winter and far into the months of spring, the creatures could not survive. All the species of them would disappear. In his undogmatic but suggestive way, Dr. Messel had added that the fact of water being an exception to the rule of fluids in relation to frost was one of the most striking evidences of intelligent design in the universe.

I recalled this discourse in contemplating the string of beads which my fly-cast had become. What had occurred to me was that the stream, instead of being water as commonly understood, H20 with a temperature not below that of the freezing-point, must be actually ice in molecular motion, ice disguised in the normal motion caused by what is known as the law of gravity. This conjecture would be confirmed if anywhere I could find solid water on the bed of the stream.

I found it.

On looking into an open patch a little below the bridge from which I had started on the journey northward up the glen, I saw, in places, the submerged ice formed ; and in others it seemed actually forming. Large stones at the bottom, stones from a foot to two feet in diameter, were, on the sides of them farthest down the stream, encrusted in ice, which seemed to be gradually adding to itself upwards, as if to envelop the whole; and shapeless masses of half-solid water, like writhing white jelly-fish, clung to other stones, shivering at the impact of the blue gush as it eddied past.

Here was an exception to the exceptional rule by which water when frozen floats. What did it mean? Had the forces of nature got beyond the control of the creative design ? For a moment one was almost tempted to think that this really might be so, especially when it was considered that seeming disorders in the processes of nature are not uncommon, as when a late snowstorm kills lambs that were born in their due time, or when premature hail suddenly devastates the orchards, undoing the long work of spring and summer; but the thought was passing. Further examination and reflection suggested a reassuring theory.

When the temperature falls below freezing-point the water in a pond does not begin to solidify immediately. First a thin layer on the surface is chilled and sinks ; then the succeeding layer is chilled and sinks ; then another; and so on until, under the influence of the cold, the whole body of water, or most of it, has been transfused within itself, and in the process has reached the freezing-point; then the forming of ice begins. Until it does begin the mean temperature of the pond is above freezing-point. That, however, could not be said of the Highland stream. Evidence to the contrary was abundant at every step. It might be an exaggeration to say that one could actually see the flanges of ice that protruded from the banks extending outwards and gradually narrowing the open space in the middle of the watercourse; but, although not literally visible, unquestionably there had been that process, which was probably continuing; for the ice could never have formed had the water not been below the temperature at which it becomes solid when still. What would have happened had this process gone on a few days longer? Soon the whole stream would have been frozen over; but there would not long have been a free channel underneath. Each day the sun at noon would have helped the running water to heave up blocks of the ice ; gradually accumulating somewhere, these would have weighed down the lowest layer ; the stream would have been dammed; distributed over a broad expanse, it would have settled quickly ; and all the way downwards from wherever the stoppage began there would soon have been no flow at all, but only a solid seam of ice.