304 



Scientific InielUgence^ 



li Chromate of lead. 



2. Carbonate of lead. 



3. Zircon. 



4. Pistazite. 



5. Carbonate of strontian. 



6. Chrysolite. 



7- Calcareous sp^r. 



8. Topaz. 



9. Tartaric acid. 



10. Rock crystal. 



11. Sulphate of copper. 



12. Selenite. 



13. Sulphate of iron. 



Some years ago Malus, a colonel of engineers in the French 

 army, announced the discovery of a new property of reflected 

 light. He found that when light is reflected at a particular 

 angle from all transparent bodies, whether solid or fluid, it has 

 acquired by reflection that remarkable property of polarization^ 

 wliich had hitherto been regarded as the effect only of double 

 refraction. 



If the light of a taper, reflected from the surface of water at 

 an angle of 52" 4b\ be viewed through a rhomboid of Iceland 

 crystal whiph can be turned about the axis of vision, two images 

 of the taper will be distinctly visible at one position of the 

 crystal. At the end of i of a revolution one of the images will 

 vanish, and it will re-appear at the end of f of a revolution. 

 The other image will vanish at the end of -|- of a revolution, and 

 will re-appear at the end of and the same phenomena will 

 be repeated in the other two quadrants of its circular motion. 

 The light reflected from the water therefore has evidently been 

 polarized^ or has received the same character as if it liad been 

 transmitted through a doubly refraetiog crystal. 



The angle of incidence at which this modification is superin- 

 duced upon reflected light increases in general with the refrac- 

 tive power of the transparent body; and when the angle of 

 incidence is greater or less than this particular angle, the light 

 suffers only a partial rnodincation, in the same manner as when 

 two rhomboids of Iceland spar are not placed eitiier in a similar 

 or in a transverse position, 



Malus found that light reflected from opaque bodies, such as 

 black marble, ebony, &c. was also polarized. But polished 

 metals, according to him, did not impress that property, though 

 they did not alter it when it had been acquired from another 

 substance. Dr. Brewster, however, has observed, that polished 

 metals polariza light as well as other substances. 



When a ray of light was divided into two pencils by a rhom- 

 boid of Iceland spar, Malus made these pencils fall on a surface 

 of w^ater at an angle of 52° AS\ When the principal section of 

 the rhomboid (or the plane which bisects the obtuse angles) was 

 parallel to the plane of reflection, the ordinary pencil was partly 

 reflected, and partly refracted, like any otlier light; but the 

 extraordinary ray penetrated the water entire, and not one of its' 



