NATURAL PPIILOSOPHT. 217 



the ether partook of the motion of the fragmentary host, and became almost 

 insensible to their pressure. It is to occurrences of this kind, which must 

 occasionally take place in the wide domains of creation, that we may ascribe 

 the appearance of temporary stars, and in doing so, we obtain a satisfactory 

 explanation of the various peculiarities which they exhibit. The existence, 

 on our own sphere, of the ether which acts so important a part in the scene 

 of celestial wonders is indicated by certain electrical phenomena. On its 

 presence seems to depend the evolution of light attending the passage of 

 electricity through the vacuum of an exhausted receiver, and the light of 

 the aurora borcalis appears to be evolved by electric action from the ethereal 

 fluid, which arrives at the polar regions from space. It is only by this hy- 

 pothesis that we can account for the effect of a shooting star during an 

 aurora, in lighting up certain parts of the vaults of heaven not previously 

 illuminated (see Humboldt's "Cosmos" on Aerolites). It thus appears 

 that the subtle medium which fills space is not to be regarded as a mere im- 

 pediment to planetary motion, but as a useful agent in the course of Nature's 

 operations, and as indispensable to our existence as the appendages of air 

 and water which roll around our planet. 



ON THE COLOR OF SALTS IX SOLUTION, EACH CONSTITUENT OF 



WHICH IS COLORED. 



The following is an abstract of a paper on the above subject, read before 

 the British Association, at its last meeting by Dr. Gladstone. 



It is a general law that " all the compounds of a particular base, or acid, 

 when in aqueous solution, absorb the same rays of light ; " hence it may be 

 deduced that when a colored base and a colored acid combine, the resulting 

 salt will transmit only those rays which are not absorbed by either constitu- 

 ent, or, in other words, only those rays which arc transmitted by both. 

 This was proved to be actually the case by a prismatic examination of com- 

 pounds of chromic, permanganic, and carbazotic acids with copper, iron, nickel, 

 uranium, and chromium. Though the compounds of chlorine, bromine, 

 and iodine with hydrogen and most metals are colorless, the compounds of 

 these halogens with gold, platinum, and palladium exhibit an absorption of 

 light due to the halogen as well as that due to the metal. The same is true 

 in respect to chlorides, bromides, and iodides of copper, iron, nickel, and 

 cobalt, when these salts are dissolved in a minimum of water ; but when 

 more water is added the color changes, and the absorption due to the halo- 

 gen no longer exists. In one or two of the cases examined a slight varia- 

 tion from the general law occurred ; and fcrrocyanide of iron forms a com- 

 plete exception. The double chloride of platinum and copper shoAvs the 

 absorbent effect of all these constituents. 



ON THE RELATIONS OF GOLD TO LIGHT. 



During the year 1856, a paper on the relations of gold to light, was rend 

 before the Royal Institution, London, by Prof. Faraday. The abstract of 



19 



