Taylor identified the critical electric potential for electrostatically forming a cone of liquid (Taylor cone-semivertical sphere) at the end of a capillary tube. The derivation began with the expression for the equilibrium state of a droplet at the end of a pressurized tube, and the coefficients for the electrostatic potential were generated by observing the deflection of charged solutions at the end of an inverted capillary. Taylor showed that the vertical voltage (V c in kV) at which the maximum jet fluid instability start, is given by 9 where H is the distance between the electrodes (the capillary tip and the collecting screen), L is the length of the capillary tube, R is the radius of the tube, and γ is the surface tension of the fluid (units: H, L, and R in cm; γ in dyne per cm). In spinning, the flow beyond the spinneret is mainly elongational. The minimum spraying potential of a suspended, hemispherical, conducting drop in air is where r is the jet radius. If the surrounding medium is not air but a nonconductive liquid immiscible with the spinning fluid, drop distortion will be greater at any given electric field and, therefore, the minimum spinning voltage will be reduced. If the electrospinning process is realized in vacuum, the required voltage will lower.