of a suspended particle and apparent slip {#suspended}
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Physical picture
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We now consider an experiment in which the above electric effects are present. We elect to use small tracer particles to probe the velocity profile, including possible fluid slip, as illustrated in Figure \[figure\]. For the same reason as for the capillary surfaces, these particles will usually be charged in solution. As they are advected by the fluid motion, they will also feel the influence of the induced streaming electric field: consequently their velocity will not only reproduce that of the fluid but will also include an induced electrophoretic component [@saville], proportional to their zeta potential and the streaming electric field. If the zeta potential of a particle has a sign opposite to that of the capillary surface, the particle will be slowed down by the electric field. On the contrary, if the particle possesses a potential of the same sign as the capillary surface, its electrophoretic component will be in the streamwise direction; furthermore, if its zeta potential is large enough, the electrophoretic velocity of the particle will be able to overcome the induced electroosmotic back-flow.

It then follows that there is a significant potential implication of 