shown by Small Particles on a Nernst Glower, 209 
Case b. — Motions of solid particles of metals and their 
oxides. These effects are so striking that we have been led 
to collect considerable data concerning them. To describe 
in detail a typical case which has already been mentioned : — 
If a sliver of cobalt, say 2 mm. long and *2 mm. thick, is 
placed lengthwise on a glower carrying direct current, at a 
temperature below the cobalt melting-point, it will slowly 
rise on end and continue turning over till it again lies flat, 
the process being repeated so that the metal as a whole moves 
along the glower against the current flow ; and the motion 
will continue till the particle stops on the cool glower terminal 
(see fig. 1). A more exaggerated case — and one which 
Fig. 1. 
shows that the forces, such as they are, must be comparatively 
large, if they are assumed to act only on the small area of 
the particle in actual contact with the glower— is that of a 
horseshoe-shaped piece of metal, say 4 mm. in diam., hung 
over the glower, with its plane at right angles to it. This 
will slowly turn (in the same sense as before) until its prongs 
point upward when it usually becomes unstable and falls off. 
In an attempt to explain these actions we have noted the 
following facts : — 
(1) The motion always reverses with reversal of current, 
and this is true no matter what the position of the particle, 
whether it is just rising from a horizontal position, or standing- 
vertical. For some metals the motion is with, for others 
against, the direction of the current, as ordinarily defined. 
In Table I., column headed " direction/' a + sign means 
motion with the current, a — sign motion against the current. 
(2) The rapidity of the . motion under similar conditions 
varies greatly in different metals. In the column headed 
*• magnitude," the numbers are roughly proportional to the 
rapidity of the motion, cobalt and copper being by far the 
best in this respect. The actual velocity of progression along 
the glower of a small piece of either of these metals would in a 
favourable case be a matter of perhaps a centimetre per 
minute. With most metals, however, the motion is so slow 
that it is practically impossible to get a progressive end-over- 
end translation of the particle along the glower ; so in taking 
