In these charts the state of the sea—whether “rough,” “smooth,” “moderate,” “slight,” etc., is marked in capital letters; and the state of the weather—as “clear,” “dull,” “cloudy,” “showery,” etc., in small letters. The direction of the wind is indicated by the arrows. Unlike the arrows of a vane, these do not point towards the direction from which the wind is coming, but are _flying_ arrows represented as moving _with_ the wind, and consequently pointing to _where the wind is going_. The force of the wind is represented in five degrees of strength. 1st. A _calm_, by a horizontal line and zero—0 thus 0; 2nd. A _light wind_, by an arrow with one barb and no feathers ______\; 3rd. A _fresh to strong breeze_, by an arrow with two barbs and no feathers ——————>; 4th. A _gale_, by an arrow with two feathers >——————>; and 5th. A _violent gale_, by an arrow with four feathers >>——————>. The temperature—in the shade—is marked in figures with a small circle to the right, indicating degrees—as 60°. These figures stand in the places where the observations are made. The other figures—usually with decimals, and placed at the end of the dotted lines—give the height of the barometer—the dotted line showing where this particular height remained the same at the time of observation. These dotted lines are called “isobars,” or _equal weights_—the weight or over-head pressure of the atmosphere being the same all along the line. What must follow from this condition of the atmosphere? Clearly a great flow or rush of air from the south towards the comparatively vacuous regions of the north. The gases of our atmosphere, like the waters of the ocean, are always struggling to find their level, and thereby the winds are produced. The air flows from all sides towards the lowest isobar. But what, then, must be the course of the wind? Will it be in straight lines towards this point? If so, a strange conflict must result when all these currents meet from opposite directions. What will follow from this conflict? A skillful physicist can work out this problem mathematically, but we are not all mathematicians, some of us are not able to follow his formulæ, and, therefore, will do better by resorting to simple observation of other analogous and familiar phenomena. A funnel or any vessel with a hole in the bottom will answer our purpose. Let us fill such a vessel with water, then open the hole, and see what will be the course of the water when it is struggling to flow from all sides to the one point of vacuity. It will very soon establish a vortex or whirlpool, _i.e._, the water instead of flowing directly by straight lines from the sides to the centre of the funnel, will take a roundabout, spiral course, and thus screw its way down the outlet of the funnel.