1 96 Mr. Hersghel on certain motions , &c. 
by M. Serrulas, is precisely as in that experiment, the cur- 
rents radiating from the point of immersion. These once 
produced, drive before them the fragment in which they 
originate, in the direction in which it exposes the greatest 
surface to their action. 
62. The attraction of the pellicle to a metallic rod plunged 
into the mercury, is also a direct consequence of the alloy of 
potassium present in the mercury, as is also the disengage- 
ment of gas from the wire. It is, in fact, precisely the expe- 
riment described in Art. 25, and has nothing whatever to do 
either with the floating fragments, or with any hydrogen 
they may be discharging at the time, farther than that their 
contact serves to furnish potassium to the mercury. 
63. It is needless, therefore, to push this examination farther, 
as all the phenomena observed by Mr. S. are only particular 
cases of those I have described. With regard to the radiant 
hydrogen producing currents by its impulse, I would ask how 
it happens that currents are produced (when the positive pole 
is placed in contact), while a thick and tough coat of oxide 
covers the whole surface ; and, one would think, must 
effectually defend it from the action of the hydrogen. Yet 
we have seen, in Art. 18, that the currents continue their 
course under this crust ; and it will hardly be contended, 
that the hydrogen finds a passage between the oxide and 
the metal. 
J F. W. H. 
London , Jan. 13, 1824. 
