shown by Small Particles on a Xernst Glower. 207 
also with silver if care was taken to protect the silver from 
direct contact with the clay surface. For in the latter case 
it would not form a globule but simply flux into and be 
absorbed by the clay surface, just as was the case when tried 
on the Nernst glower itself. 
The brightness of the flash increases with the extent of 
undercooling. Flashing appears to precede the solidification ; 
with a large drop the flash is noticeably more prolonged than 
with a small one, and very evidently occurs before the 
solidification. 
From these facts we conclude that the phenomenon is 
simply one of exaggerated undercooling made possible because 
we are dealing with a very small mass of metal which assumes 
an approximately spherical shape. Furthermore, that the 
flashing is not a direct luminescent phenomenon but is due 
to the sudden increase in temperature resulting from the 
liberation of the latent heat of fusion ; the longer duration 
of the flash in the larger globules corresponding to the greater 
amount of heat which must be dissipated. Probably, then, 
the previous observations referred to are erroneously classified 
as "luminescent." 
We have made a number of measurements of the tem- 
perature at which flashing occurs, but these seem without 
interest except to note the maximum degree of undercooling 
which has been observed, namely, about 370° C. for both 
rhodium and platinum. That is to say, rhodium, which 
melts at about 1910° C, has remained molten as low as 
15-40° C. ; and platinum, melting at 1745° C, as low as 
1370° C. 
In the case of rhodium we have observed a second anomaly 
at about 1050° C, consisting of an easily reversible change 
in the radiating power of the surface of the drop. As the tem- 
perature is lowered the drop becomes at about 1050° C. rather 
suddenly brighter — the change being seen to spread rapidly 
over the globule — and remains so (relative to the glower). 
If the temperature is again raised the reverse change takes 
place. The effect may be due to a molecular rearrangement, 
or to the absorption of some gas, but in either case the 
energy changes involved must be small, otherwise flashing 
or some similar temporary recalescent change would be 
observable. 
Phenomena of Motion of Particles. 
Quite distinct from these cases of undercooling are a 
number of cases of motion of various metals on the surface 
of the glower parallel to the current flow. The most striking 
Q2 8 
