1857.] f GM ( and other Metals) to Light. 401 



especially in that transverse to the blow, a point favourable to 

 continuity in that direction, both as it tends to preserve and 

 even reproduce it. 



If a polarized ray be received on an analyser so that no light 

 passes, and a plate of annealed glass, either thick or thin, be 

 interposed vertically across the ray, and no difference is observed 

 on looking through the analyser, the image of the source of light 

 does not appear ; but if the plate be inclined until it makes an 

 angle of from 30 to 45, or thereabouts, with the ray, the light 

 appears, provided the inclination of the glass is not in the plane 

 of polarization or at right angles to it, the effect being a 

 maximum if the inclination be in a plane making an angle of 

 45 with that of polarization. This effect, which is common to 

 all uncrystallized transparent bodies, is also produced by leaf- 

 gold, and is one of the best proofs of the true transparency of 

 this metal according to the ordinary meaning of the term. In 

 like manner, if a leaf of gold be held obliquely across an ordi- 

 nary ray of light, it partly polarizes it, as Mr. De la Rue first 

 pointed out to me. Here again the condition of true trans- 

 parency is established, for it acts like a plate of glass or water 

 or air. But the relations of gold and the metals in different 

 conditions to polarized light shall be given altogether at the 

 close of this paper. 



Deflagrations of Gold (and other metals) heat pressure, fyc. 

 Gold wire deflagrated by explosions of a Leyden battery 

 produces a divided condition, very different to that presented 

 by gold leaves. Here the metal is separated into particles, 

 and no pressure in any direction, either regular or irregular, 

 has been exerted upon them in the act of division. When the 

 deflagrations have been made near surfaces of glass, rock- 

 crystal, topaz, fluor-spar, card-board, &c., the particles as they 

 are caught are kept separate from each other and in place, and 

 generally those which remain in the line of the discharge have 

 been heated by the passage of the electricity. The deposits 

 consist of particles of various sizes, those at the outer parts of 

 the result being too small to be recognized by the h'ighest 

 powers of the microscope. Beside making these deflagrations 

 over different substances, as described above, I made them in 

 different atmospheres, namely, in oxygen and hydrogen, to 



