NATURAL PHILOSOPHY. 219 



ciently concentrated and cold, supplies a tremulous jelly ; and this, when 

 dried, yields a hard ruby gelatine, which being soaked in water, becomes trem- 

 ulous again, and by heat and more water yields a ruby fluid. The dry 

 hard ruby jelly is perfectly analogous to the well-known ruby glass, though 

 often finer in color ; and both owe the color to particles of metallic gold. 

 Animal membranes may, in like manner, have ruby particles diffused through 

 them, and then are perfectly analogous in their action on light to the gold 

 ruby glass, and from the same cause. When a leaf of beaten gold is held ob- 

 liquely across a ray of common light, it polarizes a portion of it ; and the 

 light transmitted is polarized in the same direction as that transmitted by a 

 bundle of thin plates of glass ; the effect is produced by the heated leaf as 

 well as by the green leaf, and docs not appear to be due to any condition 

 brought on by the heating or to internal structure. When a polarized ray is 

 employed, and the inclined leaf held across it, the ray is affected, and a part 

 passes the analyzer, provided the gold Him is inclined in a plane forming an 

 angle of 45 with the plane of polarization. Like effects are produced by 

 the films of gold produced from solution and phosphorus, and also by the 

 deposited dust of gold due to the electric discharge. The same effects are 

 produced by the other deflagrated metals so long as the dusty films are in 

 the metallic state. As these finer preparations could be held in place only 

 on glass or some such substance, and as glass itself had an effect, it was 

 necessary to find a medium in which the power of the glass was nothing ; 

 and this was obtained in the bisulphide of carbon. Here the effect of gold 

 upon the ray of light which was unaffected by the glass supporting it was 

 rendered very manifest, not only to a single observer, but also to a large 

 audience. The object of these investigations was to ascertain the varied 

 powers of a substance acting upon light, when its particles were extremely 

 divided, to the exclusion of every other change of constitution. It was 

 hoped that some of the very important differences in the action upon the 

 rays might in this way be referred to the relation in size or in number of the 

 vibrations of the light and the particles of the body, and also to the distance 

 of the latter from each other ; and as many of the effects are novel in this 

 point of view, it is hoped that they will be of service to the physical phi- 

 losopher. 



As to the quantity of gold in the different films or solutions, it can at 

 present only be said that it is very small. Suppose that a leaf of gold, 

 which weighs about O2 of a grain, and covers a superficies of nearly ten 

 square inches, were diffused through a column having that base, and ~2 -7 

 inches in height, it would give a ruby fluid equal in depth of tint to a good 

 red rose, the volume of gold present being about the one five hundred thou- 

 sandth part of the volume of the fluid ; another result gave O'Ol of a grain 

 of gold in a cubic inch of fluid. These fine diffused particles have not as 

 yet been distinguished by any microscopic power applied to them. 



PHOTOHELIOGEAPH. 



Under the auspices of the Royal Society, G. B., a photographic apparatus 

 for registering daily the position of the spots upon the sun's disc, as sug- 



