08 On the Properties of Electric Waves. 



(1) Serpentine. — This substance, which appears fibrous, 



transmits the ordinary and the extraordinary ray, 

 with unequal intensity. A fairly thick piece com- 

 pletely absorbs vibrations parallel to the fibres, and 

 transmits vibrations perpendicular to the fibres. 

 Ordinary radiation, after transmission through a 

 thick piece of serpentine, would be plane-polarized, 

 the vibration taking place perpendicular to the 

 fibres. A thick piece of serpentine thus acts as an 

 efficient polarizer. 



There are certain important points in connexion 

 with selective conductivity and the phenomena of 

 polarization by absorption exhibited by certain sub- 

 stances, which will be dealt with in a future paper. 



(2) Nemalite. — This crystal exhibits this effect in a still 



more marked degree. 



(3) Tourmaline also produces the depolarization effect. 

 The difference in absorption of the ordinary and the 

 extraordinary rays is, however, not so great as in the 

 case of light. 



(4) Beryl, Apatite, and Barytes are also very good 

 crystals for exhibiting the depolarization effect. 



Polarization Produced by other Substances. — I found many 

 other natural substances producing polarization, the most 

 interesting being vegetable fibres. Common jute (Corchorus 

 capsularis) exhibits the property in a very marked degree. 

 1 cut fibres of this material about 3 cm. in length, and built 

 with it a cell with all the fibres parallel. I subjected this cell 

 to a strong pressure under a press. I thus obtained a com- 

 pact cell 3x3 cm. in area, and about 5 cm. in thickness. 

 This was mounted in a metallic case, with two openings about 

 2x2 cm. on opposite sides for the passage of the radiation. 



This cell was found to quench vibrations parallel to the 

 fibres, and transmit vibrations perpendicular to the fibres. 

 Jute cells could thus be made to serve as polarizers or 

 analysers. 



- Effect due to Strain. — Could be exhibited by stratified 

 rocks, the plane of stratification being inclined at 45° to the 

 horizon. 



Effects similar to that produced by unannealed glass can 

 be imitated by a block of unequally chilled paraffin. 



The polarization-apparatus described above may also be used 

 as a polarimeter, the rotation of the analyser being measured 

 by the graduated disk. 



