779 
of Edinburgh, Session 1871 - 72 . 
I reserve farther developments of this subject until I have made 
a sufficient number of experiments with both junctions at high 
temperatures,, particularly when these are two of the series of 
neutral points ; and especially until I mana'ge to settle, by one at 
least of several processes which have occurred to me, whether the 
multiple neutral points depend upon peculiarities in the behaviour 
of the iron, or of the platinum, or of both. 
[Added during 'printing . — I have since made out that the lines 
of the diagram are approximately straight, and parallel to the lead 
line, for the platinum metals, that of hard platinum being below the 
lead line, while those of most of the other alloys are above it, and 
that the multiple neutral points depend upon the peculiar sinuosity 
of the line for iron. I have also obtained curious results of a some- 
what similar kind with steel wire. The method I employed was 
to^explore the part of the thermo-electric diagram included between 
the lines of gold and palladium, by making a multiple arc of these 
two metals, and varying the ratio of their separate resistances. But 
I reserve details until I have carefully examined the behaviour of 
nearly pure iron.] 
2. On a Method of Exhibiting the Sympathy of Pendulums. 
While making some magnetic experiments lately with Mr Fox 
Talbot, I happened to notice that two equal rectangular pieces of 
tin plate, when standing nearly parallel to one another on the pole 
of a large electromagnet, acted on one another so that a vibration 
communicated to either was in a few seconds handed over to the 
other, and vice versa. 
The definiteness of the result led me to try the experiment with 
ordinary bar magnets. Taking two large magnetised bars of almost 
exactly equal mass, I suspended them with their axes in the same 
horizontal line, so that their (small) vibrations were executed in 
that line, their undisturbed periods being very nearly equal, and 
the distance between them (when at rest) so small compared with 
their lengths, that we need consider only the magnetic action of 
the two poles nearest together. With this apparatus the transfer 
of energy from one pendulum to the other is most beautifully 
exhibited, for if one only be in motion at starting, the magnets 
