688 
Proceedings of the Boyal Society 
The observations were made in the following manner : — A key 
was introduced into the battery circuit, and as the melted metal 
gradually cooled down, this key was depressed at regular intervals 
of thirty seconds, and the deflection of the galvanometer noted. In 
most of the experiments the temperature was taken at the same 
time by means of a copper-iron thermo-electric junction which had 
been previously tested, and of which one junction was inserted into 
the melted metal, while the other was kept at a constant tempera- 
ture. 
The results of experiments conducted in this manner on tin and 
lead are given in a table at the end of this communication, and 
indicate a very sudden and considerable alteration in the conduc- 
tivity of these metals at their melting points. It may be mentioned 
that the tin employed in the experiments was commercial grain tin ; 
the lead was in the form of assay foil. 
Soon after commencing these experiments it occurred to us to 
employ Hose’s fusible metal, in consequence of the ease with which 
it can be melted. The result which we obtained was, to us, quite 
unexpected ; for the resistance, instead of becoming suddenly about 
half its former amount as the metal solidified, descended to its lower 
value by three successive falls. The experiment when repeated 
gave the same result. 
We therefore resolved to investigate further into the matter, and 
proceeded to form alloys of lead and tin. To make sure that, if the 
same appearance should present itself in these alloys, it might be 
referred to some property of the alloy, the conductivity of specimens 
of the lead and tin used in making them up was tested; in every case 
the resistance altered by a single change from its one value to 
the other. 
The alloys were made by melting the proper amounts of lead and 
tin in a ladle or in a crucible, sometimes a flux was added, and a 
considerable number of specimens of each alloy was made, that the 
results given by any one specimen might be checked by those ob- 
tained from the others. In the two alloys of tin and lead which 
were employed, the metals were fused together in quantities which 
were simple multiples of their atomic weights; but this is not 
necessarily the only manner in which the metals may be mixed in 
order to form an alloy. This is well brought out in a paper by 
