---+-----+---+---------+----+------------------------------------------- With (_a_) similar wind and weather will continue. „ (_b_) winds will veer towards west. „ (_c_) „ „ east. „ (_d_) „ „ north. „ (_e_) „ „ south. “The probable strength of wind will be in proportion to the rate of increase of statical force, or differences of barometrical readings. The position of least pressure must be carefully considered; as, in accordance with the law, the wind will blow around that locality. The same remark applies to areas of high pressure, which, however, very rarely occur in a well-defined manner over the British Isles.” Referring to the table on page 76, the scale 0 to 6 was formerly used by meteorological observers at land stations, and it was intended to express, when the square of the grade was obtained, the pressure of the wind as given in the second column. “The velocity is an approximation as near as can be obtained, from the values assigned by Neumayer, Stow, Laughton, Scott, Harris, James, &c.”[15] [Footnote 15: Strachan’s “Portable Meteorological Register,” 4th edition.] Few meteorological axioms are better established than that which embodies the fact that “every wind brings its weather,” and the primary cause of wind being the motion of the air induced by rarefaction, it is obvious that there is a constant tendency for the equatorial and polar currents in any locality to establish an equilibrium, and this consideration is found to facilitate weather predictions for extended periods. Thus, in consequence of the unusual prevalence of _east_ winds in the spring of 1862, a wet summer was predicted. The prediction was fully borne out by an incessant continuance of _south-west winds_, with clouded skies and the usual accompaniment of deluges of rain. These winds continuing, with slight intermissions only, till the spring of the following year, less than the usual number of south-west winds was looked for during the summer; the result fully justified the anticipation, the summer of 1863 being fine and warm, especially during the earlier portion. Similarly, without committing the inaccuracies of Murphy in 1838, the summer of 1877 may be reasonably expected to be a dry and cool one from the long continuance of warm and wet months in the winter of 1876-7. The scientific research and mechanical ingenuity directed of late years to producing trustworthy estimates of the direction, pressure, and velocity of the wind, have resulted in the production of a series of instruments, possessing great precision and accuracy. [Illustration: 54. Wind Vane. Scale about 1/20.] The _direction_ of the wind is indicated by vanes, a very efficient form of which is shown at Fig. 54, the _velocity_ by revolving cups, and the _pressure_ by the pressure plate and by calculation from the known velocity.