button to main menu  Clarke's Survey of the Lakes, 1787

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page xli:-
kinds of weather, though the resistance of similar winds from neighbouring hills may prevent its being taken notice of.
It may be remarked of this wind, that it generally blows from Cross-fell longest in the Spring, when the sun has somewhat warmed the air beneath, and does not cease till it has effectually cooled it: thus it sometimes continues for a fortnight or three weeks, which I consider as a peculiarity of the Helm-Wind of Cross-Fell. As such therefore, though I have not leisure to attempt the discussion of its various phaenomena, such as that of the bar, &c. I hope I shall not do a thing unpleasant to the philosophic reader, if I attempt to give an account of its general cause, which I shall do on the following simple principles.
The chymists know, that evaporation produces cold, and that of AEther is remarkable enough. To those who have not seen their method, or heard of it, I shall mention that of the brewers, who throw quick-lime into their large cauldrons when they want to cool them suddenly; and the effect, I apprehend, depends upon similar principles, though exhibited in a different manner: any man, however, may have a cheap proof of the cold produced by evaporation, by plunging his hand into water, and holding it up to the sun or wind, or both, at any season, to dry. Even waving all these as causes of the cold to be expected from vapours, the fogs hovering upon rivers are a sensible proof that the thing is so; which any one must have experienced still more forcibly, who has met with a rainy cloud, or a mere fog, upon the mountains in warm weather, and will have felt that such a cloud, even at a distance, can obtrude a piercing cold upon the warmest day in Summer. Now, whether it is by attraction, (which I think it is,) or any thing else, that hills detain clouds which wander in the region of their summits, belongs not to my purpose, since it is a thing known universally to exist wherever there are hills: and Cross-fell, probably from its vast length, height, and loneliness, is peculiarly powerful in detaining them; for it intercepts many, and there is no hill near whose attraction, or effects upon the winds, &c. may serve to remove them: thus they gather not into that shadowy indiscriminate mass of vapours which settle on hills before and during rains, but such as I have described. It will be easily conceived, from what is premised, that such an assembly of vapours will produce a proportional degree of cold around it; whereas the height of any hills in Britain, without such a cause, or a brisk wind, is not sufficient to produce any great degree of it. I have felt a suffocating warmth on the tops of some of them in a calm day, even when drifts of snow still remained, and were far beneath me. Such cold, therefore, must occasion a corresponding density in that portion of air on which it operates; and when the sun, by that more-continued action of his rays which belongs to valleys, has warmed the air in the country beneath in the day, or left it so in the evening, that air must be proportionally rarefied; and becoming lighter than that in a higher region, or at least lighter with respect to its situation, the equilibrium which fluids wish to preserve will consequently be interrupted: the higher air will thenceforward rush down to keep up this equilibrium, and in its course occasion the wind of which we are speaking.
I believe this account will correspond with all the circumstances attending the Helm-Wind of Cross-Fell. I think it necessary to mention again, that it blows until it has entirely cooled the air of the adjoining country, (for itself is very chill,) and is almost always terminated by a rain, which restores, or to which succeeds a general warmth, and into which the Helm seems to resolve itself.
  weather forecasting
It may also be an amusement to the traveller, to take notice of the old-fashioned modes of foretelling the different kinds of weather yet in use amongst the rustics of every part, notwithstanding the general introduction of barometers; for it is by these only that they know, with any degree of certainty, what the rising or falling of the mercury indicates. The inhabitants of every mountainous tract have greater numbers
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