Editor's reply to Mr. Fiske about the Fiske-Mott insulator

Re Fiske-Mott Insulator.

[With reference to Mr. Fiske's letter in our last issue, in the absence of comparative tests, we still adhere to our opinion with reference to the efficiency of the above insulator. That an unusually high degree of insulation may be obtained by a material which has the power of repelling moisture in a high degree, or at least of preventing its forming a continuous film over the surface of the insulator, we are not prepared to deny ; but we must repeat that the result of practical experience, in this country at least, has conclusively proved that the notion that a diminished surface of contact improves the insulation is fallacious. We know of one form of insulator, indeed, in which the principal of small surface contact is carried out, and to a much greater extent than in the Fiske-Mott pattern—in fact, the contact in the case we refer to is at one point only, and not at several—but the result has not proved a success ; in fact the insulator is at its best but a very indifferent one. Mr. Fiske's statement that "The leakage of ten insulators on a telegraph line is about ten times that of one insulator, because the area of contact is about ten times as great" is not a correct one. The leakage is ten times as great because there is ten times the amount of surface for the current to leak over. It is, in fact, the whole surface of the insulator which determines the value of the insulation, and not the area of contact of the wire. In making our statement, it must be observed that we do not suggest a theory which practice may possibly prove to be correct, but we start from actual known facts, and merely put forward our theory to explain the cause. Our theory may be wrong, but this in no way affects the correctness of the facts.—EDS. ELEC. REV.]