  We present the experimental performance of a 91-actuator deformable mirror
made of a magnetic liquid (ferrofluid) using a new technique that linearizes
the response of the mirror by superposing a uniform magnetic field to the one
produced by the actuators. We demonstrate linear driving of the mirror using
influence functions, measured with a Fizeau interferometer, by producing the
first 36 Zernikes polynomials. Based on our measurements, we predict achievable
mean PV wavefront amplitudes of up to 30 {\mu}m having RMS residuals of
{\lambda}/10 at 632.8 nm. Linear combination of Zernikes and over-time
repeatability are also demonstrated.
