SCIENTIFIC SUMMARY. 
281 
mass, adhering to the sides. The tube was cut through at this point and 
the black mass was pulverized, when some parts were noticed to be extremely 
hard. On closer examination these parts were found to be mostly trans- 
parent, and on triturating them, they were obtained free from the black 
matter. They turned out to be crystalline carbon, exactly like diamond. 
From over eighty experiments made with these tubes, Mr. Hannay obtained 
only three results of a successful nature. The diamond fragments were burnt 
in a current of oxygen and found to contain 97*85 per cent of carbon. It 
appeared in some further experiments as if the diamond carbon contained a 
little nitrogen chemically combined with it. 
Artificial Formation of Scorodite. — A concentrated solution of arsenic 
acid was heated with iron wire in a closed tube to 140°-150°C. The wire 
was found, by Verneuil and Bourgeois, to be covered in a few hours with a 
gray, apparently amorphous, material, which soon filled the whole of the 
fluid. This substance is a mixture of amorphous iron arseniate, and arsenious 
acid in small crystals. When the heating is continued, this material disap- 
pears gradually, and is changed slowly into scorodite ; while fresh, apparently 
amorphous, material is formed, and this is continued till the solution of arsenic 
acid becomes too weak to continue the reaction. This goes on for about eight 
days. The crystals, in composition, specific gravity, density, and crystalline 
form, agree in every respect with the natural crystals of scorodite. ( Compt. 
Fend. 1880, xc. 223.) 
PHYSICS. 
Silver Films in the Camera lucida form the subject of a suggestion by 
Mr. J. C. Douglas to the Asiatic Society of Bengal. He points out that 
instruments of this kind are divisible into two classes, the opaque and the 
transparent. To the former belong Wollaston’s and Soemmering’s ; to the 
latter the tinted glass reflector. The former are fatiguing, the latter liable 
to indistinctness, from double reflection at the two surfaces of the glass plate. 
Silver films, on the other hand, are so highly reflective that two or more 
successive reflections may be used. The thickness of the film may, moreover, 
be modified according to the ratio desired between reflected and transmitted 
light, and the films may be applied on curved as well as on plane surfaces 
They may also be found useful in constructing microscopic illuminators. 
A New Action of the Magnet on Electric Currents forms the subject 
of a communication to the American Journal of Mathematics, by E. H. Hall. 
It was proposed to show, that if the current of electricity in a fixed conductor 
is attracted by a magnet, the current should be drawn to one side of the 
wire, and, therefore, the resistance experienced should be increased. To test 
this theory, a flat spiral of German-silver wire was enclosed between two 
thin discs of hard rubber, and the whole placed between the poles of an 
electro-magnet in such a position that the lines of magnetic force should pass 
through the spiral at right angles to the current. The wire was about 
•§ millim. in diameter, its resistance about 2 ohms. The magnet was 
worked by a battery of twenty Bunsen cells, joined four in series and five 
abreast. The strength of the magnetic field was probably 15,000 or 20,000 
