of Edinburgh, Session 1881 - 82 . 
373 
same phenomena are noticed, the only difference being that they 
run along the upper instead of the lower surface of the tube. 
The diagram representing them is seen in fig. 3. 
In the case of spheres which are of the same specific gravity, or 
which differ only very slightly from the specific 
gravity of the liquid in which they are immersed, 
the relationship is quite different. Here specific 
gravity being alike between spheres and liquid, one 
of the forces which formerly acted upon the 
sphere is removed, and the only force now acting Fig. 3. 
upon it is horizontal, and is represented by the strata of liquid. 
The friction is least at the centre of the tube, greatest at the 
periphery. The pressure is greatest where the resistance is 
least. Such spheres, of specific gravity equal with the liquid, 
always, therefore, tend to be pressed into the centre of the stream. 
Hence, the smaller they are the faster they will 
circulate , because the small sphere comes in contact 
only with the swift filaments of liquid in the axis, 
while the larger it is the more it becomes arrested 
in its movement by the slow strata at the peri- 
phery of the tube. This is represented in fig. 4. 
Discs show exactly the same phenomena, the only qualification 
being, that when they are lighter or heavier than the liquid they 
sometimes tend to fall over on their side rather than run on their 
edge, and this of course creates a fallacy. When they are of 
specific gravity equal with the liquid it does not matter how they 
lie. 
The lighter and heavier spheres, further, rotate , while those of 
equal specific gravity with the liquid have the gliding motion of 
the coloured blood-corpuscles. The former come in contact with 
the wall of the tube, the friction against which causes them to 
rotate ; while the latter not touching the tube wall, instead of 
rotating, have a smooth gliding motion. 
Experiments with numbers of finely divided bodies in a capillary 
tube, such as those employed by Schklarewsky (Pflliiger’s Archive , 
i., 1868), are fallacious in many respects, specially in the fact that 
the exact relationship between the specific gravity of each particle 
and the liquid in which it is immersed is not known. Capillary 
