1895 - 96 .] Dr Beattie on Thermo-electricity in Bismuth. 149 
VIII., IX., X., XI., XII., XII., the R given in column 4 may 
be taken as holding for all field strengths, for bismuth and the 
other alloys this is not the case, R given can only be used for the 
field given, for the other fields its value is quite different, being 
larger for weak fields, smaller for strong ones ; and in the bismuth- 
lead alloys it has a different sign even, according as the field is 
weak or strong. Taking all these things into consideration, it still 
remains true that the rotatory coefficient of an alloy cannot be 
calculated from those of its component metals. 
On the other hand, a glance at column 4 shows us that a con- 
ductor, with an extreme thermo-electric position, has a large trans- 
verse effect. So far as the direction of the effect is concerned, we 
have here no exceptions. Thus, in Plates XII., XIII., instead of 
a negative effect due to the presence of bismuth, we have, in both 
cases, large positive effects comparable in magnitude with that of 
pure bismuth. With regard to the magnitude, the thermo-electric 
position of the Plates I., II., III. explain why it is we have in 
them such a large negative effect. At the other end of the series 
beyond antimony, we have, in Plates IX., X., XI., XII., XIII., 
positive effects greater than in antimony, and in numerical value of 
the same order of magnitude as in bismuth. 
Here, however, there are irregularities. In Plates VIII., IX., 
X. the effect is smaller than we might expect, and in XIV. it is 
larger. 
Leduc has also observed that the transverse effect in an alloy of 
equal parts of bismuth and lead is less than in silver. The posi- 
tion of this alloy in the thermo-electric series is next silver. 
Hall also has observed that in alloys of copper and zinc the 
transverse effect is nearer that of copper than the composition of 
the alloy would lead us to expect. The thermo-electric position of 
these alloys is also nearer copper than the composition would lead 
us to expect. 
To determine in which direction experimental effort should next 
be directed for the purpose of examining whether a relation 
between thermo-electricity and the transverse effect exists, we must 
remember that the latter is a function of the magnetisation and of 
the temperature. So far we have considered only cases where the 
temperature was approximately constant and the field variable ; 
