the question whether any great inequal 
existed in a metallic wire, it being obvious that.such imequality 
might exist, without being ordinarily apparent. Iron wire of 
about one twentieth of an inch in diameter was first tried. ‘Two 
parallel wires were connected at the ends, and made to form part 
of a galvanic circuit, (fig. 2.) One of these was then divided 
into several equal parts, and for each Fig. 2. 
of the points of division, a point of P x 
equal electric tension was found in 
the other, by extending a conductor from the point in the first 
wire through the galvanometer to the second, and passing along 
the latter till the needle ceased to be deflected. The points thus 
determined in the second wire, were very nearly equidistant. 
Brass wire was tried in a similar manner, and with the same re- 
sult. For the convenient performance of these and the subse- 
quent experiments, two slides were used to move on the con- 
ducting wires, carrying in contact with them bits of brass wire 
crossing at right angles. ‘These latter wires were connected with 
the galvanometer by metallic ribands, one of which was divided 
in the middle, so that the connection could be made and broken 
at pleasure. ‘This was done with wooden handles, to prevent 
the disttirbance which was found to arise from thermo-electricity, 
if the hand touched the conducting ribands. 
7. For the course of experiment already indicated, No. 22 
brass wire was used. © T’o a piece of board were attached bridges 
A, B, C, (fig. 3,) and on these were strained several pieces of the 
wire, as shown in tle figure, ab being a single wire, which we 
ak Fig. 3. 
may call the gauge ; 
others ed of about two feet, and four ef of over three feet. These 
wires were insulated from one another by the dry wood, except 
when soldered to pieces of sheet copper P, O, N, passing under 
the bridges. With this arrangement, the experiments could be 
conveniently varied, by leaving more or less of the wires out of 
Seconp Serizs, Vol. I, No. 2.—March, 1946. 30 
