Sir Humphry Davy oh the connection between 
Repulsion (indicated by the needle) will cause the gdhanic ap- 
paratus to revolve round the prolonged axis of the wire ah. 
If we substitute, in place of the conducting wire, a large rib- 
bon of copper of the same breadth as the plate of zinc, a feebler 
effect only is produced. The effect is on the other hand in- 
creased by making the conductor very short. 
Fig. 8. represents the perpendicular section of this arrange- 
ment, in the direction of the breadth of the trough ; and 
Fig. 9. is a perspective view of it, in which abed ef represents 
the conducting plate, and c z zf the plate of zinc. Here the 
north pole of the needle will be attracted towards the plane of 
a be, and the south pole will be repelled from the same plane ; 
ccZ/will have contrary effects. In this apparatus the extremi- 
ties act like the poles of the needle, but it is only the faces of 
the extremities, and not the intermediate parts that have this 
analogy. 
A moveable galvanic apparatus may also be made of two 
plates, one of copper and one of zinc, twisted into spirals, and 
suspended in the conducting fluid. This apparatus is more 
moveable, but greater precautions are necessary to avoid decep- 
tion when experiments are made with it. 
I have not yet discovered a method of making a galvanic ap- 
paratus direct itself towards the poles of the earth. For such 
a purpose the apparatus would require to be much more move- 
able. 
Account of Sir Humphry Davy's Experiments. 
In repeating the interesting experiments of M. Oersted, Sir 
Humphry Davy found j that the uniting wire of platinum was 
magnetic from its power of attracting iron filings. This wire Was 
also found to communicate permanent magnetism to steel bars 
transversely attached to it, or placed transversely at some distance 
from it ; while the same bars, when placed parallel to the wire^ 
had only a temporary magnetism when in the vicinity of the ap- 
paratus. 
The most important fact, however, in Sir Humphry Davy’s 
experiments, is, that when the electricity from a Leyden battery 
h passed through a wire or through air^ the wire and air and the 
