78 Intelligence and Miscellaneous Articles. 



strong and the conductors are sufficiently close together, the lower 

 part becomes dissemhiated and converted into a plume ; a brilliant 

 light like that of the ordinary spark is then observed at the two 

 extremities of the conductors ; this light gradually dininishes as it 

 advances towards the middle, whilst the plume becomes developed 

 round it, so that it might be said that the spark, starting from the 

 extremities, becomes converted by degrees into a plume, in such a 

 way that the internal parts are the last to undergo this change. 



With two iron or steel wires, small globes of reddish light are 

 seen darted in all directions, probably due to particles of metal de- 

 tached or projected by the discharge, and ignited in the air. This 

 ]n'oves that the electric spark not only transports matter, but also 

 projects it in all directions. 



When the electricity is passed between two very acute points, 

 such as those of two small sewing needles, a great part of the elec- 

 tricity passes almost continuously from one point to the other, but 

 at the same time a great number of sparks are seen rapidly uniting 

 with the luminous thread which exists between the two conductors. 

 These small sparks are recognized principally at the luminous points 

 formed at the places from which they start ; and it is remarkable 

 that these points are always at a certain distance from the apex of 

 the pointed conductor. 



On attentively observing the extremities of the spark, a very 

 luminous point is seen in each, surrounded by a halo, the diameter 

 of which is sometimes greater than that of the spark, and which 

 acquires different appearances according to the nature of the metal 

 of which the conductors are composed. 



The halo is small and white with platinum points ; it is blue with 

 iron, and of a line green with copper ; lastly, with two wires of 

 amalgamated metal, very large white haloes, with but little bril- 

 liancy at their margins, are obtained. These haloes are much 

 larger and more brilliant if the metals between which the spark is 

 produced be covered with a stratum of olive oil. This result is 

 easily obtained by placing at the two extremities a drop of oil 

 which covers a small portion of the wires, and causes the passage 

 of the spark from points at a greater distance but nearly in contact 

 with the oil, so that they are constantly covered with a layer of 

 that liquid. By operating in this way with very fine copper wires, 

 the brilliant points are surrounded by two large haloes of a mag- 

 nificent green colour, which produces a very pretty effect of contrast 

 with the violet colour of the spark. The cause of this large halo is 

 probably the combustion of a small quantity of oil, the flame of 

 which contains metallic particles detached by the spark. Lastly, it 

 must be observed that with other isolating liquids more combustible 

 than oil, such as oil of turpentine, the phsenomenon is not so well 

 produced. — // Nuovo Cimento, vii. p. 182; Bibl. Univ. de GetCeve, 

 May 20, 1858, p. 38. 



ON THE ORIGIN OP FELSPARS, AND ON SOME POINTS OP 

 CHEMICAL LITHOLOGY. BY T. STERRY HUNT. 



In a communication to the Royal Society of London, read on the 



