weather maxims, the result of observation and experience, have always been current, and the value of many of these is now recognised and explained by science. The first step towards acquiring an insight into the causes which control our weather is a study of the laws which regulate the flow and changes of the winds in these islands. The air is the great medium in which all the changes of weather are elaborated. We live at the bottom of a great ocean of air, which extends for many miles upwards, and which is always heaving and changing, like the other ocean which it covers. The winds, which are the ever-changing currents which flow through this invisible sea, are, roughly speaking, the principal factors in the making of the weather. Many of us know very well the general character of the weather which accompanies the wind from the principal points of the compass, that which comes from the moist warm south-west, for instance; or with the blustering, shower-bringing north-wester; or with the harsh, dry, east wind in spring; but to most of us the wind itself ‘bloweth where it listeth.’ The movements of the air and changes of the wind are, however, subject to laws, a knowledge of which is in some degree necessary before we can understand how our weather is made for us. A simple definition of the wind which we ordinarily experience is that it is air obeying the force of gravity, in seeking to return to an equilibrium which has been disturbed. By the aid of the barometer we are able to form some idea of what is constantly taking place in the great ocean above us. The principle upon which this simple and useful instrument is constructed is easily understood. The air presses downwards upon the earth’s surface with a weight averaging nearly fifteen pounds to the square inch. If a portion of the surface of any fluid is relieved from this pressure by inverting over it a tube exhausted of air, the weight of the air upon the surface outside will force the fluid up into the tube until the weight of the column counterbalances the pressure which the air would exercise upon the amount of surface covered by the mouth of the tube. A column of mercury in such a case will rise in an air-exhausted tube to a height of about thirty inches; while water, from its lighter specific gravity, rises to a height of about thirty-four feet before it counterbalances the weight of the air above. The depth, and consequently the pressure, of the air overhead is, however, constantly varying within certain limits; and the column of mercury in the barometer enables us to keep a faithful record of the movements of the waves of air in the great ocean under which we live. At times, the depth of air above us is comparatively shallow, and the pressure beneath is lessened; the column of mercury is not raised so high, and the barometer is said to fall. At other times, the air is heaped up in particular places; the pressure beneath is increased, and the barometer is said to rise.