It may further be remarked of this wind, that it is very irregular, rarely occurring in the summer months, and more frequent from the end of September to May. It generally blows from Cross-Fell longest in the spring, when the sun has somewhat warmed the earth beneath, and does not cease till it has effectually cooled it; thus it sometimes continues, according to Mr. Ritson, for a fortnight or three weeks, which he considers a peculiarity of the Helm wind of Cross-Fell. The wind 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. The best explanation of this very interesting and remarkable phenomenon is given in the following observations of Dr. T. Barnes of Carlisle. The air or wind from the east ascends the gradual slope of the eastern side of the Penine chain or Cross-Fell range of mountains, to the summit of Cross-Fell, where it enters the Helm or cap, and is cooled to a low temperature; it then rushes forcibly down the abrupt declivity of the western side of the mountain into the valley beneath, in consequence of the valley being of a warmer temperature, and this constitutes the Helm wind. The sudden and violent rushing of the wind down the ravines and crevices of the mountains occasions the loud noise that is heard. At a varying distance from the base of the mountain the Helm wind is rarified by the warmth of the low ground, and meets with the wind from the west, which resists its further course. The higher temperature it has acquired in the valley, and the meeting of the contrary current, occasion it to rebound and ascend into the upper region of the atmosphere. When the air or wind has reached the height of the Helm, it is again cooled to the low temperature of this cold region, and is consequently unable to support the same quantity of vapour it had in the valley; the water or moisture contained in the air, is therefore condensed by the cold, and forms the cloud called the Helm-Bar. The meeting of the opposing currents beneath,--where there are frequently strong gusts of wind from all quarters, and the sudden condensation of the air and moisture in the Bar-cloud, give rise to its agitation or commotion, as if "struggling with contrary blasts." The Bar is therefore not the cause of the limit of the Helm wind, but is the consequence of it. It is absurd to suppose that the Bar, which is a light cloud, can impede or resist the Helm wind; but if it even possessed a sufficient resisting power, it could have no influence on the wind which is blowing near the surface of the earth, and which might pass under the Bar.