347
OF ENGINEERING FOliMULÆ.
Electrical Formula, by Paget Higgs, LL.D., C.E.—
continued.
time may be more accurately measured than by
any mechanical chronograph, it being arranged
that during the time t the condensei: is made to
discharge through r, its potentials (P) before and
after (p) being measured in the ordinary manner.
46. Table of Resistances at 0° C. (Jenkiu.)
Wire, 1 ft. Weighing 1 grain. Oue metre weighing 1 gramme One foot by *OoiV diameter. One mfetre by 1 mm. diameter.
Silver, annealed .. 0'2214 0'1544 9-936 0’01937
„ haid drawn 0-2421 0-1689 9-151 0'02103
Copper, annealed .. 0'2064 0-1440 9-718 0'02057
„ hard drawn Gold, annealed .. 0'2106 0-1469 9-910 0’02104
0-5849 0’4080 12-52 0-02650
„ hard drawn .. 0’5950 0-4160 12-74 0*02697
Aluminium, an- J nealed .. .. 5 *0'0682 0-0576 17-72 0-03751
Zinc, pressed .. .. 0-5710 0-3983 32-22 0-07244
Platinum, annealed 3’536 2'464 55-09 0'1166
Iron, annealed .. 1-2425 0-7522 59-40 0’1251
Nickel, annealed .. 1*0785 0-8666 75'78 0-1604
Tin, pressed .. .. I-317 0’9184 80'36 0-1701
Lead, pressed .. 3’236 2-257 119’39 0-2527
Antimony, pressed 3’324 2'3295 216-0 0-4571
Bismuth, pressed .. 5-054 3-525 798'0 1-689
Mercury, liquid .. 18'740 13-071 600'0 1’270
Platinum-silver 1 (usual alloy) J German silver . • 4-243 2-959 143-35 0-3140
2'602 1-850 127-32 0'2695
The resistance of silver varies about 0 • 377 per
cent for lö C. at 20c 0., of copper 0‘388 per cent.,
of mercury '072 per cent., of platinum-silver ‘031
per cent., and of German silver 'Oil per cent.