152 
DE. FAEADAY ON THE EXPEEDIENTAL EELATIONS 
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, no difference 
is observed on looking through the analyser, the image of the source of hght does not 
appear ; but if the plate be inclined until it makes an angle of from 30° to 45°, or there- 
abouts, 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 inclina- 
tion be in a plane making an angle of 45° with that of polarization. This effect, which 
is common to all unciystallized 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 ordinar}- 
meaning of the term. In like manner, if a leaf of gold be held obhquely across an ordi- 
nary ray of light, it partly polarizes it, as Mr. De la Eue fii’st pointed out to me. Here 
again the condition of true transparency is estabhshed, for it acts hke 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, &c. 
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 par'- 
ticles, arrd rro pressure in any directiorr, either regular or irregular, has been exerted upon 
them iir the act of division. When the deflagrations have been made near suriaces 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, aird gerrerally those which remain in the 
lirre of the discharge have beerr heated by the passage of the electricity. The deposits 
corrsist of particles of various sizes, those at the outer parts of the result being too small 
to be recognized by the highest powers of the microscope. Beside making these defla- 
gratioirs over different substances, as described above, I made them in different atnro- 
spheres, namely, in oxygen and hydrogerr, to compare with ah ; but the general effects, 
the colours produced, and the order of the colours, were precisely the same in all the 
cases. These deposits were insoluble in nitric acid and in hydrochloric acid, but in the 
mixed acids or in chlorine solution were soluble, exactly in the manner of gold. There 
is no reason to doubt that they consisted of metallic gold in a state of extreme diHsion. 
Now as to the effects on light, ^. e. as to the coloured rays reflected or transmitted by 
these deposited particles, and first, of those in the line of the discharge where the wh'e 
had been. Here the mica was found abraded much, the glass less, and the rock-crystal 
and topaz least. Where abraded, the gold adhered ; in all the other parts it could be 
removed with the shghtest touch. The gold deposited m this central place was metallic 
and golden by reflected light, and of a fine ruby colour- by transmitted light. On each 
side of this line the deposit had a dark colour, but when particularly examined gave a 
strong golden metallic reflexion, and by transmission a fine -violet coloiu*, partaking of 
green and ruby in different parts, and sometimes passing altogether into green. Beyond 
this, on each side, where the tints became paler and where the particles appeared to be 
