Conduction of Galvanic Electricity through Moist Air, 205 
current passed from plate to plate through the India rubber cloth, 
When however the battery consisted of twenty compound pairs, a 
slight current passed, as indicated by a delicate galvanoscope. I 
made no further investigation or application of this fact till 1843, 
when recurrence was had to this feature to solve some difficulties 
experienced in the projection of a line of Morse’s teleZraph be- 
tween this place and Baltimore. Ten miles of lead pipe contain- 
ing four well insulated wires had been laid in the ground, and upon 
trying these wires respectively, making the wire one half of the 
circuit, and the lead pipe the other half, with a battery of inten- 
sity, a current could be established through any one of the three 
extra wires. Being consulted by Prof. Morse as to the probable 
cause of this cross firing as it was technically called, the solu- 
tion seemed to me to be obvious in view of the above experi- 
ment. The reasoning was sufficiently plausible to induce Prof. 
Morse to abandon the undertaking of the pipe, and resort to 
his original plan of raising the wire upon posts. The expla- 
__ hation was simply this, viz. that the insulating or non-conducting 
Material would under any circumstances conduct the current; 
but in some cases, the amount transmitted could not be apprecia- 
ted by any known test however delicate, was a postulate subse- 
quently borne out. Does not stich a conclusion follow directly 
from the law of Pouillet, that the conducting power of wires is 
directly as their cross section and some inverse ratio of their 
length, in connexion with the well established laws of the dif- 
ferent conducting powers of metals? For example, copper hav- 
ing from four to six times the conducting power of iron, a wire 
of iron, to equal in this respect a wire of copper, should be of 
from four to six times the size. Let this rule be applied to poor- 
_ & conductors, and we may infer that the poorest conductor, or 
what has been usually considered a non-conductor, would become 
4 conductor, if the area of its cross section were indefinitely in- 
creased and its length remained nearly nothing. In the case of 
the wires in the lead pipe—the one for instance joining the two 
Poles of the battery—is separated from that lying next to 1t and 
the lead pipe, by a layer of thin non-conducting material through- 
out its length; and if we suppose the width of this layer in con- 
tact to be + of an inch, the length of ten miles would give a sur- 
face of 550 square feet, while the length of the conductor would 
be only the thickness of the material, and a constant quantity, 
Secoyp Szaizs, Vol. II, No. 5.—Sept-, 1846. 
