The Magnetic Anisotropy of Rubber

In experiments on the magnetic properties of some crystals, one of these cystals was suspended between the poles of a small electromagnet. These poles were flat and of the same diameter as the cores (5 cm.), while the air gap varied from 1.5 to 4 cm. and the field at the center from 8800 to 5500 gauss units. The crystal was suspended by a silk thread with very slight twist and a small rubber ring cut from a piece of gas tubing. It was observed that, as soon as the electric field was set up, the assembly oriented itself strongly, and the couple exceeded the magnitude which was expected. It was observed also that this couple continued when the crystal was removed and only the rubber ring remained as a possible cause of the phenomenon. The same phenomenon is observed with a ring of paramagnet rubber and with a ring of diamagnetic rubber, whether the rubber is supple or whether it has become brittle, and whether the ring is perfect or whether it has a cut in it. Instead of flat rings, longer sections of tubing, e.g., 2 to 3c m. long, can be suspended in the magnetic field. It is then particularly surprising to observe that the pieces of tubing always orient themselves axially in the magnetic field, whereas under the same conditions elongated isotropic substances orient themselves in this way only if they are paramagnetic.