436 Mr. E. H. Hall on the Rotation of the 
In looking about for an explanation of this disagreement, I 
found that the thickness of the strip had been called :00104 cm. 
in 1881, and 0012 cm. in the later experiments. The former 
estimate was obtained by weight, the latter by measurement 
with calipers. The difference accounts well enough for the 
different values obtained for the R. P. Which estimate of the 
thickness is the more reliable I will not undertake to decide. 
Summary. 
10% R.P. at 20° C. 
Copper . . . . —820 
Zico iis ames 1-820 
Four alloys of copper and zine were tested. Ifa series be 
made beginning with zinc and ending with copper, the four 
alloys being ranged between according to composition, the 
series thus formed will be the same as that obtained by 
ranging these metals and alloys according to the algebraic 
magnitude of their R. P.’s. In the alloys, however, the R. P.’s 
are algebraically somewhat nearer that of copper than might 
be expected from the composition. 
Troi.) a Mie eicte oes 
R. P. nearly constant through wide range of magnetic 
intensity, but apparently decreasing slightly at high inten- 
sities. 
No ascertained permanent effect. 
Steel, soft se eet L20GO: 
Permanent effect about 5 per cent. of temporary effect. 
Steel, tempered . +88000. 
Permanent effect about 1} per cent. of temporary effect. 
Gold (no new test of magnitude of R. P.) . —660 
No ascertained permanent effect. 
CoWaltacuie mae + 2460. 
Nickel ane — 14740. 
Bismuth . . —8580000. 
Antimony. . +114000. 
A fall of 1° C. in temperature causes 
in the R. P. of Iron, a fall of 3 per cent. approx. 
Steel, soft, x 4 i 
Steel, temp’d, _,, 4 55 
Cobalt, zm dl 3 
Nickel, 2 
) 3 7) 
Non-magnetic metals, apparently a small 
increase. 
