The properties of conductors, more particularly of metals, have been so frequently examined, that the literature of the subject is appallingly heavy. In what follows I have endeavoured to keep clear of what might properly appear in a treatise on electricity on the one hand, and in a wiring table on the other. The most important work on the subject of the experimental resistance properties of metals has been done by Matthieson, Phil. Trans. 1860 and 1862, and British Association Reports (1864); Callender, Phil. Trans. vol. clxxiii.; Callender and Griffiths, Phil. Trans. vol. clxxxii.; The Committee of the British Association on Electrical Standards from 1862 to Present Time; Dewar and Fleming, Phil. Mag. vol. xxxvi. (1893);
Klemencic, Wiener Sitzungsberichte (Denkschrift), 1888, vol. xcvii. p. 838; Feussner and St. Lindeck, Zeitsch. fuer Inst. 'Kunde, ix. 1889, p. 233, and B. A. Reports, 1892, p. 139. Of these, Matthieson, and Dewar and Fleming treat of resistance generally, the latter particularly at low temperatures.
[Footnote: The following is a list of Dr. Matthieson's chief papers on the subject of the electrical resistance of metals and alloys: Phil. Mag. xvi. 1858, pp. 219-223; Phil. Trans. 1858, pp. 383-388 Phil. Trans. 1860, pp. 161-176; Phil. Trans. 1862, pp. 1-27 Phil. Mag. xxi. (1861), pp. 107-115; Phil. Mag. xxiii. (1862), pp. 171-179; Electrician, iv. 1863, pp. 285-296; British Association Reports, 1863, p. 351.]
Matthieson, and Matthieson and Hockin, Klemencic, Feussner, and St. Lindeck deal with the choice of metals for resistance standards. Callender's, and Callender and Griffiths' work is devoted to the study of platinum for thermometric purposes.
The bibliography referring to special points will be given later. The simplest way of exhibiting the relative resistances of metals is by means of a diagram published by Dewar and Fleming (loc. cit.), which is reproduced on a suitable scale on the opposite page. For very accurate work, in which corrections for the volumes occupied by the metals at different temperatures are of importance, the reader is referred to the discussion in the original paper, which will be found most pleasant reading. From this diagram both the specific resistance and the temperature coefficient may be deduced with sufficient accuracy for workshop purposes. In interpreting the diagram the following notes will be of assistance. The diagram is drawn to a scale of so-called "platinum temperatures" — that is to say, let R0, R100, Rt be the resistances of pure platinum at 0°, 100°, and t° C. respectively, then the platinum temperature pt is defined as
pt = 100 X (Rt-R0)/(R100-R0)
This amounts to making the temperature scale such that the temperature at any point is proportional to the resistance of platinum at that point. Consequently on a resistance temperature diagram the straight line showing the relation between platinum resistance and platinum temperature will "run out" at the platinum absolute zero, which coincides more or less with the thermodynamic absolute zero, and also with the "perfect gas" absolute zero. Platinum temperatures may be taken for workshop purposes over ordinary ranges as almost coinciding with air thermometer temperatures. The metals used by Professors Dewar and Fleming were, with some exceptions, not absolutely pure, but in general represent the best that can be got by the most refined process of practical metallurgy. We may note further that the specific resistance is only correct for a temperature of about 15° C., since no correction for the expansion or contraction of material has been applied.
The following notes on alloys suitable for resistance coils will probably be found sufficient.