the coldest-south-west the warmest. North-west are intermediate, with a northerly character; and south-east, with a southerly character.[1] The winds, therefore, may be divided as in the following diagram:
- ↑ The dew-point can never be higher than the temperature of the air. Supposing, therefore, during the winter in the high regions of Lapland, Sweden, and Norway, the temperature of a breeze to be 20° or 24° F., often doubtless very much lower, air of that temperature cannot hold vapour higher than 20° or 24°. This atmosphere being put in motion, and rushing rapidly to the southern and warmer regions, is constantly acquiring a higher temperature, but passing over only a limited tract of ocean, it acquires but little increase in its vapour; the dew-point, consequently, remains very nearly the same.
Let us suppose that such a breeze has reached the temperature of 82° or 34° when arriving at the British Isles, the difference between this and the dew-point (20° or 24°) would constitute a very dry harsh wind, little likely to be accompanied with any deposition; on the contrary, drying up all the moisture it meets with, it would have precisely the character of our north-east winds in a very marked degree. On the other hand, a south-west breeze coming from the warmer regions and over an immense tract of ocean, into the colder temperature of Britain, would soon become cooled, until the temperature of the air was no greater than the temperature of the vapour it bears with it or the dew-point. At this point, and pursuing still its northerly course, some of the vapour must be precipitated, or take the shape of cloud, in either of which cases it parts with that portion of its temperature which was necessary to its invisible condition, and this is im-
