Intelligence and Miscellaneous Articles. 395 



are still smaller, we see that the repulsion with them would be 

 considerably greater than the attraction ; hence particles of dust 

 whose radii are smaller than the thousandth of a millimetre would 

 repel, at a temperature of 0° in space, with a force the order of 

 whose magnitude is a million times greater than that of the 

 Newtonian attraction. 



If we take the radii still smaller, we come gradually to molecular 

 dimensions. Our formula (8) is, however, no longer applicable 

 to individual molecules, since they are not perfectly black, and 

 both their dimensions and their respective distances in bodies are 

 small compared with the wave-length of the radiation ; the action 

 of two molecules on each other must therefore, like that of two 

 resonators, be treated in a complex manner. 



If equation (8) does not give us the direct action of two mole- 

 cules, it reminds us that in investigations of the nature of what 

 are called " molecular forces " we cannot, without more ado, 

 neglect the forces arising from the reciprocal radiation of the 

 molecules, without having first defined what fractions of the mole- 

 cular forces they form. — Wiedemann's Annalen, No. 2, 1892. 



AN ELECTKOLYTIC EXPERIMENT. BY LEO ARONS. 



If a copper cylinder is placed in an electrolytic cell which con- 

 tains copper-sulphate solution between two copper electrodes, part 

 of the current sent through the cell will disperse in the cylinder. 

 In the places at which the lines of flow T enter the cylinder copper 

 is deposited, while an equivalent quantity is dissolved at the places 

 where they emerge. If the copper cylinder is arranged so that it 

 rotates easily about a horizontal axis, it will begin to rotate as soon 

 as the current is closed, since the part opposite the anode is heavier, 

 the other lighter. As the conductivity of the copper so greatly 

 exceeds that of the liquid, we can use a hollow cylinder without 

 any material diminution in the number of lines of flow which pass 

 through the metal. Erom this circumstance a considerable mo- 

 bility of the cylinder can be attained, even when the bearings of 

 the axle are very roughly worked. The thickness of the hollow 

 cylinder can be easily so calculated that the cylinder, which is closed 

 at the ends, floats in a concentrated solution of copper sulphate, 

 but sinks in water ; accordingly it is possible to attain a degree of 

 concentration in which the cylinder only just sinks, and thus 

 exerts scarcely any pressure on the bearings. 



The small apparatus which I used consisted of a longish glass 

 vessel of rectangular section. The copper cylinder, which 

 occupied almost the whole breadth of the trough, was 4*5 centim. 

 in length and its diameter was 10 centim. The thickness of the 

 sides was 1*8 millim. At the ends ebonite plates were cemented, 

 and through them passed the axis, a glass rod 1 millim. in dia- 

 meter, which projected a f ew r millimetres on each side ; the bear- 



