ELECTEICAL PRINCIPLES OP THE ATLANTIC TELEGRAPH. 417 
the language commonly used in describing these phenomena,, 
is called the “ passage of an electric current. - ^ On the other 
hand, it is found that the most perfect “ non-conductors/ - ’ or 
“ insulators, - ” as they are also called, do not entirely prevent 
the propagation of the electrical condition. Hence, instead of 
regarding conductors and non-conductors as bodies of essen- 
tially different properties, it is more correct to think of both 
as opposing resistance to the passage of electric currents, this 
resistance being small in the case of conductors and relatively 
very great in the case of non-conductors or insulators. 
And it is found, further, that when any particular piece of 
wire of any particular material is taken as a standard of com- 
parison, the resistance of a wire of the same material and of 
the same thickness, but of twice the length, is twice as great 
as that of the standard ; while the resistance of a wire of the 
same length, but of twice the thickness, is only half as great 
as that of the standard. That is to say, the resistance of a con- 
ductor of any given material is directly proportional to its length, 
said inversely proportional to its thickness, or cross-section. 
When we thus conceive of all bodies as resisting or opposing 
the passage of electric currents, it becomes at once self-evident 
that, when a current flows from any one point to any other, it 
will not necessarily follow the shortest distance between the 
two points, but its path will be determined by the line of least 
resistance. The two poles of a galvanic battery are two points 
between which there is a tendency to the interchange of elec- 
tricity — in other words, to the formation of an electric current. 
But if the only connection between them is made (say) by a 
piece of gutta-percha, the only path offered for the passage of 
the current is one which opposes to it so much resistance, that 
no current of appreciable strength is produced ; if, however, a 
thin copper wire is extended from one pole to the other, this 
will offer a path of much less resistance than the gutta-percha, 
and consequently a perceptible current will be established 
along it, even though it may be many times longer than the 
gutta-percha ; and again, if a thick wire be also added, a path 
of still smaller resistance will be offered to the current, and 
the consequence will be that, although the current in the thin 
wire will not be arrested, the electricity will chiefly follow the 
easiest path, and the thick wire will carry a current just as 
many times stronger than that in the thin wire, as its resist- 
ance is smaller than that of the latter. 
We now see what the first part of the problem was which 
had to be solved in order to establish an electric telegraph 
between Ireland and Newfoundland. This problem may be 
stated thus : given the two poles of a galvanic battery at 
Yalentia, it was required to provide a path from one to the 
