1 72 Mr. Herschel on certain motions produced in 
In the acids, particularly in the more powerful and concen- 
trated ones, and such as are good conductors of electricity, 
they are decided and violent. In saline solutions their force 
is less, in proportion as the electro-positive energy of the 
base is greater. Thus, in the salts with a basis of potash they 
are feeble, and often only perceptible by a momentary start 
of the mercury when the circuit is completed. In those of 
soda, ammonia, baryta, strontia, and lime, they are more dis- 
tinct, while in salts of magnesia, alumina, and the metallic 
oxides, their influence is still more sensible. On the other 
hand, under solut : ons of the pure alkalies and alkaline earths, 
the mercury remains quite quiescent, or at most is only agi- 
tated by feeble and irregular motions, depending on causes 
not now in contemplation. 
1 7. In many liquids, and especially in solutions of the nitrates, 
there is formed not only a current radiating from the negative 
pole, but also one from the positive, which even has in some 
cases a preponderance over the other. These co-exist in the 
mercury ; and, in consequence of their action, a zone of equi- 
librium is formed in the globule, nearer to one or the other 
pole, as the antagonist current is more or less violent. The 
best way to render the influence of this counter-current sen- 
sible, is to operate on a large quantity of mercury, under 
dilute solutions, keeping the negative pole at a distance, and 
the positive very near. In this way there are few liquids 
which, when the pile is in good action, do not show some 
signs of a counter-current from the positive pole. The cause 
of this will be evident, when we come to speak of the action 
of metallic alloys. 
1 8. If either pole be brought in contact with the mercury, no 
