260 MAGNETIC INFLUENCE 



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 forte, heat; and 

 we may safely refer many meteorological phenomena 

 to similar alterations of condition in the atmosphere, 

 relative to the magnetic relations of the aerial cur- 

 rents. 



That magnetism has a directive power is satisfactorily 

 shown by the formation of crystals in the neighbourhood 

 of the poles of powerful magnets. The common iron 

 salt, the proto-sulphate, ordinarily crystallizes so that 

 the crystals unite by their faces ; but when crystallizing 

 under magnetic influence, they have a tendency to 

 arrange themselves with regard to each other so that 

 the acute angle of one crystal unites with one of the 

 faces of another crystal, near to, but never actually at, 

 its obtuse angle. In addition to this, if a magnet of 

 sufficient power is employed, the crystals arrange them- 

 selves in magnetic curves from one pole to the other, a 

 larger crop of crystals being always formed at the north 



good and distinct results. Sulphurous acid gas is diamagnetic 

 in air. Muriatic acid gas was decidedly diamagnetic in air. 

 On the Diamagnetic Conditions of flame and Gases : Philosophical 

 Magazine, 1847, p. 409. 



