588 HISTORY OF SCIENCE. 



refer to his discovery of Dia-magnetism, because it showed magnetism to 

 be a universal property. It was formerly supposed that only iron, cobalt, 

 nickel, and compounds of these metals, exhibited magnetic properties. 

 Towards the end of the eighteenth century the question was raised 

 whether all bodies might not be affected by magnets ; and some of the 

 observations made about this time were sufficiently remarkable, but 

 they failed to attract attention. Thus, it was found that a piece of 

 bismuth is repelled by both poles of powerful magnets. Coulomb in 

 1812 noticed that slender wires of gold, silver, etc., or slender rods of 

 glass delicately suspended between the poles of a powerful magnet, 

 placed themselves at right angles to the lines joining the poles. In 

 1828 it was announced that certain substances, bismuth especially, 

 repelled the poles of delicately-suspended magnetic needles. Up to 

 1845 these observations remained merely isolated facts, and they at- 

 tracted but little notice. In the year just named Faraday discovered 

 the influence of magnetism on polarized light. Thus, for example, 

 when through a certain kind of glass occupying the centre of a coil a 

 ray of polarized light is passed, the plane of polarization is, when the 

 current is turned on, deflected in the same direction as the current. This 

 led Faraday to examine the action of the magnetic forces on the glass 

 itself, which was composed of lead with boric and silicic acids. He 

 suspended a bar of the " heavy glass " by a silk fibre between the 

 poles of a magnet. The glass bar was by no means indifferent to the 

 magnetic forces, but instead of coming to rest in the direction of the 

 line joining the magnetic poles, as a piece of iron would have done, 

 it assumed a direction at right angles to this. We have here Cou- 

 lomb's observation repeated. But Faraday extended his experiments 

 to all kinds of substances, whether solid, liquid, or gaseous, and the 

 result was that he was able to announce the law of magnetic action 

 as affecting all substances whatever. All bodies admit of division into 

 two classes : first, magnetic bodies, which are attracted by the magnet, 

 and settle in the direction of the line joining the poles ; second, dia- 

 magnetic bodies, which are repelled by both poles and are turned across 

 the line joining the poles. The first division contains(inaddition to iron, 

 nickel, cobalt, and manganese) several metals whose magnetic proper- 

 ties had not been suspected before Faraday's investigation, such as 

 platinum, palladium, etc. The compounds of these metals are gene- 

 rally also magnetic. Among gases oxygen gas is strongly magnetic. 

 In the dia-magnetic division are bismuth and certain other metals, the 

 non-metallic elements, such as sulphur, phosphorus, carbon, etc. The 

 same is the case with nitrogen, hydrogen, carbonic acid, and many 

 other gases. Water, alcohol, essential oils, and most other liquids 

 not being solutions of metallic salts are dia-magnetic. Animal sub- 

 stances come under the same class. 



Very powerful magnets must be used in order to make manifest 

 the general magnetism and dia-magnetic properties of all bodies. It 



