Phenomena of the Capillary Electroscope. 



99 



solution beneath it lie?, constitutes a fulcrum upon which the moving 

 layers of liquid mechanically act. If it were possible to suspend the 

 mercury in the midst of a large mass of a liquid electrolyte of its own 

 specific gravity, the effects would probably be greatly modified, and 

 there would be very little translation of the mass of mercury (com- 

 pare Herschel's paper, section 10, p. 167). 



In the experiments by Armstrong, also those of Quincke and Jiir- 

 gensen, of the mechanical transfer of liquids by the passage of electric 

 currents through slender columns of them in tubes, the axial portion 

 of the liquid was observed to move in an opposite direction to the 

 outer layer. This inner moving portion, or that farthest away 

 from the surfaces of adhesion, may be regarded as the return current. 



It is generally considered that the surface layer of particles of 

 every solid and liquid is in a state of mechanical tension, and con- 

 sequently that every mass of such substance, even that which is only 

 of microscopic magnitude, may be crudely viewed as being bounded 

 by a more or less tightly-fitting envelope. This circumstance also 

 appears to be related to the phenomenon of motion of the mercury. 

 The surface tension of that metal appears to be lessened at the 

 positive mercurial electrode, and increased at the negative one in 

 nearly all electrolytes. As there is also a surface tension of the liquid 

 as well as that of the mercury, the primary motion is probably a 

 resultant of the two. According to this view there exists two modes 

 by which an electric current may vary the surface tension of a con- 

 ductor in contact with an electrolyte, the one being attended by 

 electrolysis, and the other not. If it were simply a. result of diminu- 

 tion of surface tension of the mercury by the passage of an outgoing 

 current, then it ought not to vary in direction by variation of liquid, 

 strength of liquid, or diameter of tube. 



As adhesion influences so greatly the action of the instrument, 

 perfect freedom from dust is a most important condition of success, 

 and the most effectual way of securing this is to insert the capillary 

 tube in the pressure- chamber as soon as it is made, and fill it at once 

 with clean mercury. Multitudes of points of adhesion are met with in 

 tubes which have long been open to the atmosphere. The pressure 

 tube should also be completely freed from dust by previously agitating 

 successive portions of mercury in it. Dust, not moisture, is the great 

 source of failure. Adhesions of the mercury do not usually interfere 

 unless they happen to be within the range of movement of the 

 meniscus. 



The influence of friction I have not examined ; it plays, however, 

 an important part in the practical use of the instrument. 



7. Relations of the Movements to Seat and Temperature. 



As heat, applied to the junction of mercury and an electrolyte, 



h 2 



