180 REPORT—1863. 
TABLE (continued). 
Conducting | Percentage de- 
power crement in con- 
at 0°. ducting power 
between 0°& 100° 
Saver Wil o p-c. platimum™ » 2... sv. sles ss 31:64 11:3 
Silver, with 9-8 p.c. platinum*® ............ 18:04 * fot 
Copper, with 9°7 p.¢. tim ...0.. 0 se eeeeeree 12:19 6-6 
ie eold-ailver alloy * : ccc oss see os 15:03 6:5 
Platinum, with 33°4 p.c. iridium....,....... 4:54 5:9 
Copper; With US pict tin ee Aa Oks soe 10°21 5:2 
Gold, with 18-1 p.c. silver and 15-4 p.c. copper* 10°6 5:2 
Gold, with 15:2 p.c. silver and 26-5 p.c. copper* 12:02 4:8 
GPM I peti en sidlete see gy poo dod od a ste © oho 7°80 4-4 
Gold, willl pt UEOR- Ue ie tsicc scales dee eee 2°10 43 
Goldy sptiRaery 6 fats a Geis a aloe ee 2:37 3°8 
Silver, with 25 p.c. palladium.............. 8°52 34 
Silver, with 33-4 p.c. platinum+............ 6:70 31 
It will be observed that I have not yet been able to find an alloy whose 
conducting power decreases between 0° and 100° less than that of the alloy of 
silver with 33-4 p.c. platinum; and from results obtained in this direction 
in conjunction with Dr. Vogt, I am of opinion there will be great difficulty 
in doing so. We have already tested upwards of 100 alloys, and it is curious 
how few we haye found whose conducting power varies less than that of Ger- 
man silver between 0° and 100°. 
Apprnpix 0.—On the Elementary Relations between Electrical Measurements. 
By Professor J, Crerk Maxwein and Mr. Freemine Jenkin. 
Part I.—Lyrropucrory. 
1.- Objects of Treatise.—The progress and extension of the electric telegraph 
has made a practical knowledge of electric and magnetic phenomena necessary 
to a large number of persons who are more or less occupied in the construc- 
tion and working of the lines, and interesting to many others who are un- 
willing to be ignorant of the use of the network of wires which surrounds 
them. The discoveries of Volta and Galvani, of Oersted, and of Faraday are 
familiar in the mouths of all who talk of science, while the results of those 
discoveries are the foundation of branches of industry conducted by many 
who have perhaps never heard of those illustrious names. Between the 
student’s mere knowledge of the history of discovery and the workman’s 
practical familiarity with particular operations which can only be communi- 
cated to others by direct imitation, we are in want of a set of rules, or rather 
principles, by which the laws remembered in their abstract form can be 
applied to estimate the forces required to effect any given practical result. 
We may be called on to construct electrical apparatus for a particular 
purpose. In order to know how many cells are required for the battery, and 
of what size they should be, we require to know the strength of current 
required, the electromotive force of the cells, and the resistance of the circuit. 
If we know the results of previous scientific inquiry, and are acquainted with 
the method of adapting them to the case before us, we may discover the 
proper arrangement at once. If we are unable to make any estimate of what 
is required before constructing the apparatus, we may have to encounter 
* Proc. Roy. Soc. xii, 472, 1863, Tt Brit, Assoc, Report, 1862, p. 187. 
