130 COILS-QUANTITY OF ELECTRICITY.

the earth, so that any of the electricity transmitted, as itescapes from the wire, may he intercepted by this commu-nication with the earth, and so transmitted direct to the earthwithout the possibility of its entering an adjoining wire.

In such case it will only be necessary in very great lengthsof wire and in very adverse weather to increase the quantityof electricity transmitted, in order to make due allowance forthe quantity that escapes at the points of the insulation. How-ever great such amount of electricity required may be, noportion thereof can reach the adjoining wire and thereby dis-arrange the telegraphic instruments connected with such otherwires.

COILS.

With respect to the diameter and length of the wires to beemployed in surrounding the electro-magnets, or the magnetsto be used in the telegraphic instruments, these must he madeto suit the particular length of the circuit and the size of theelectro-magnets or permanent magnets employed, as well asthe kind of galvanic battery and the number of cells thereinintended to be used.

Each telegraph will require a separate calculation, in whichthe resistance of the circuit and the battery itself will form anelement. No precise rule therefore can be given, but thewhole will depend on the proper solution of the equation aspropounded by Professor Ohm, and given at page 110. Theengineer who is acquainted with the laws of this science willfind no difficulty in the solution of the problem, whereas tothe public, or to those ill-versed in the arcana of the science ofelectricity, it would be impossible to make the solving of thisproblem intelligible.

QUANTITY OF ELECTRICITY TO BE USED FORTELEGRAPHING.

Many persons even well conversant with the electric tele-graph have considered that the sole end to be obtainedwas to devise a telegraphic instrument in which the smallest