Note 47 — APPENDIX II. On the Variation of Electric Resistance at a Point of Imperfect Contact in a Circuit.

The term “semi-conductor” is very rarely used by electricians, who prefer the term “partial conductor” as being more correct. Moreover, electricians, from Faraday downwards, are practically agreed in calling plumbago a good conductor, and worthy of being classified by reason of its high conductivity along with the metals. The substances known as “semi-conductors” are those given in Ferguson’s ‘Electricity,’ p. 49 (edition of 1873), namely, alcohol, ether, dry-wood, marble, paper, straw, and ice. Mascart and other eminent authorities agree in this classification. It would tax even Mr. Edison’s unrivalled ingenuity to make of these materials a transmitter that should alter its resistance by pressure!