In this paper, it is shown that if two spheres of equal radii are
placed axisymmetrically in a steady Stokes stream, separation of the
flow from the spheres occurs if the distance between their centres
is less than approximately 3-67 times the sphere radius. For spheres
whose spacing is less than this value, wakes form on both spheres
and the fluid within the wakes moves in closed eddy type motion.
When the distance between the centres of the spheres is less than
approximately 3.22 times the sphere radius, a cylinder of fluid
links both spheres, and within this cylinder the fluid rotates in
one or more ring vortices, the number of vortices increasing as the
distance between the spheres is decreased. When the spheres are in
contact, the fluid rotates in an infinite set of nested ring
vortices.