We still search in the dark, and see but dimly the evidences; yet it becomes almost a certainty to us, that this stone of granite, with its curious arrangement of felspar, mica, and quartz, presents its peculiar condition in virtue of some law of magnetic force. The crystal, too, of quartz, which we break out of the mass, and which presents to us a beautifully regular figure, is, beyond a doubt, so formed, because the atoms of silica are each one impelled in obedience to one of these two conditions of magnetism to set themselves in a certain order to each other, which cannot be altered by human force without destruction. All the laws which regulate the forms of crystals and amorphous bodies are, to the greatest degree, simple. In nature the end is ever attained by the easiest means; and the complexity of operation, which appears sometimes to the observer, is only so because he cannot see the spring by which the machine is moved. The gaseous envelope, our atmosphere, is in a neutral state. Oxygen is strikingly magnetic in relation to hydrogen gas, whilst nitrogen is as singularly the contrary; and the same contrasts present themselves when these gases are examined in their relation to common air. Thus, oxygen being magnetic, and nitrogen the contrary, we have an equilibrium established, and the result is a compound neutral in its relations to all matter. All gases and vapours are found to be diamagnetic, but in different degrees.[191] This is shown by passing a stream of the gas, rendered visible by a little smoke, within the influence of a powerful magnet. These bodies are, however, found relatively to each other,--or even to themselves, under different thermic conditions,--to change their states, and pass from the magnetic to the diamagnetic class. Heat has a very remarkable influence in altering these relations; and atmospheric air at one temperature is magnetic to the same fluid at another: thus, by thermic variations, attraction or repulsion may be alternately maintained. By this it must be understood that a stream of air, at a temperature elevated but a few degrees above that of an atmosphere of the same kind into which it is passing, is deflected in one way by a magnet; whereas, if the stream is colder than the bulk through which it flows, it is bent in another way by the same force. In this respect magnetism and diamagnetism show equally the influence of another physical force, heat; and we may safely refer many meteorological phenomena to similar alterations of condition in the atmosphere, relative to the magnetic relations of the aërial currents.