25 8 SCIENTIFIC RECREATIONS. 



Professor Faraday in his memorable experiments divided a long list of 

 different substances into para-magnetic and dia-magnetic bodies. He 

 classed them under these two heads, according as they took up a certain 

 position parallel or perpendicular to the axial or equatorial line. This 

 definition of " dia-magnetic " was " a body through which the lines of 

 magnetic force are passing, and which does not by their action assume the 

 usual magnetic state of iron or loadstone." He concluded that all bodies 

 were magnetic, and by suspending a great number of various substances he 

 found they placed themselves axially, that is, lying between the poles of 

 the magnet, or equatorially, viz., at right angles to that line. If the 

 magnets be suspended at each side the same bodies will assume a position 

 with their longest diameters between the poles, while others will be repelled 

 by the magnets even if the poles be reversed. So those bodies which are 

 attracted and lie in the axial line are termed para-magnetic ; those 

 repelled into the equatorial line are termed dia-magnetic. In the " Proceed- 

 ings of the Royal Society for 1846," Faraday's account of the various 

 experiments can be studied in detail. We can only give a brief resume of 

 them here ; and he showed that the motions displayed by dia-magnetic 

 bodies in a magnetic field are all reducible to one simple law viz., that 

 the particles of the dia-magnetic tend to move into the positions of the 

 weakest magnetic force. 



He experimented upon a large number of bodies and gases ; he tested 

 crystals, metals, liquids, and solids, and proved in whatever state a body 

 might be in the effect was the same ; whether simple or compound, it made 

 no difference. Of course in a compound the preponderance of the dia-mag- 

 netic or para-magnetic property would influence the result, and the medium 

 in which the body operated on was placed, was a condition in the experi- 

 ment. He proved that if a body be suspended in a medium or surrounded 

 by a medium whose power either way is stronger than the body, that 

 body is para-magnetic or dia-magnetic, according as it is surrounded by a 

 medium whose power is weaker or stronger than the body itself. The 

 arrangement of the bodies is as follows, from the para-magnetic to the 

 dia-magnetic, bismuth being the most dia-magnetic of all : 



PARA-MAGNETIC METALS. DIA-MAGNETIC. 



Iron. Cerium. 



Nickel. Titanium. 



Cobalt. Palladium. 



Manganese. Platinum. 



Chromium . O smium. 



Bismuth. Sodium. Gold. 



Antimony. Mercury. Arsenic. 



Zinc. Lead. Uranium. 



Tin. Silver. Rhodium. 



Cadmium. Copper. Iridium, etc. 



Common air was also discovered to have a magnetic action, and hot air 

 is more dia-magnetic than cold. Oxygen is as para-magnetic in the air as 

 iron is on the earth, and this, it was considered, may give rise to magnetic 

 storms, and account for the declination of the needle. 



We may now proceed to consider the Mariner's Compass. The 

 compass, or the mariner's compass, is so common that it is scarcely necessary 



