A text-book of electricity in medicine and surgery for the use of students and practitioners.

  • Poore, George Vivian, 1843-1904.
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of electricity in medicine and surgery for the use of students and practitioners. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

    28/316 (page 12)
    plate of the series are united by a good conductor. When the two terminals are united by tbe conductor the circuit is said to be closed, and electrical action takes place. When they are not so united the circuit is said to be open, and electrical action ceases. We have said that the various elements and the terminals must be united by a good conductor, and this brings us to speak of conductors and of non-conductors. There are certain bodies which electricity traverses with greater or less ease—such are the metals, charcoal, acid liquids, and the animal body—and these are called conductors. There are, again, certain bodies which electricity traverses with the greatest difficulty—such as resins, gutta-percha, baked wood, and porcelain—and these are called non- conductors or insulators, because, when a conductor, charged with electricity, is surrounded by a non-conductor, the electricity with which the conductor is charged cannot escape, or, in other words, it is insulated. There is, however, no conductor so perfect but that it offers some resistance to the passage of the current. Con- ductors differ enormously—caderis paribus—in the resistance which they oppose to the current. The metals are the best conductors, and the best of the metals in this respect are silver, copper, and gold. Hence it is that copper, from its cheapness and low resistance, is so largely employed in the manufacture of galvanic batteries and conductors. The re- sistance offered by the metals varies very much, and it has been found that the resistance offered by lead and mercury is respectively about ten times and fifty times as great as that offered by copper. The resistance of the best conducting liquids is vastly greater than that of metals. In round numbers, the resist- ance of dilute sulphuric acid is a million times, and that of a solution of sulphate of copper is ten million times, greater than that of pure silver. It is important to bear in mind that we have to do with