Prof. Challis on a Theory of Galvanic Force, 433 



be anticipated that the action between a solid and a fluid would 

 be considerable, on account of the dissimilarity of their super- 

 ficial molecular conditions. If a chemical affinity exists between 

 the solid and the fluid, the disturbance may be expected to be 

 still greater, because such affinity exhibits itself by a tendency 

 in the superficial action so far to disturb the atoms as to put 

 them into new relations. The action' between two gases (as 

 oxygen and hydrogen) which tend to combine might produce 

 sensible secondary currents, while no such effect would follow 

 from the contact of two gases (as oxygen and nitrogen) which 

 have no chemical affinity. These are, in short, facts of experi- 

 ence which are at once seen to be in accordance with the theory, 

 if it may be assumed that the secondary tetherial currents of the 

 theory are the same as the galvanic currents of experiment. 



On this assumption the theory explains the fact that sub- 

 stances which generate galvanic currents are good conductors of 

 electricity, and exhibits the connexion of the development of 

 electricity with the generation of the currents. 



3. It appears from experiment that different substances have 

 different powers of transmitting galvanic currents. There are 

 conductors and non-conductors of galvanism, as of electricity; 

 and, generally, the substances which conduct electricity also 

 conduct galvanic currents. Air is a non-conductor as well of 

 galvanic currents as of electricity. The ratio of the two con- 

 ductive powers does not appear to be the same for different 

 substances. It does not belong to the present theory to inquire 

 into the reasons for these facts, which are mentioned here only 

 because they bear upon the subsequent explanation of the 

 hydrodynamical theory. 



For instance, it may be asked, if the origin of galvanic cur- 

 rents be such as the theory indicates, why do not the same 

 attractions and repulsions of light bodies take place in the 

 neighbourhood of the voltaic battery as in the neighbourhood of 

 a body whose electricity is excited by friction ? To this I reply 

 that the induced electricity at any point of the voltaic battery is 

 very much feebler than the electricity induced when the original 

 disturbance of the superficial atoms is caused by friction, and 

 the currents due to a feeble induction are proportionally feeble. 

 Any perceptible motive power of partial currents, acting through 

 the air, may be prevented by the non-conductiveness of the air 

 itself, and the insulation of the battery. But when the separate 

 streams excited at a great number of points (as in a large 

 battery consisting of numerous cells) are, as it were, concen- 

 trated in an electrode of fine wire, considerable motive power 

 acts through the air, as is evident by the known action of such 

 electrodes on each other when, being arranged so as to be near 



