of a second fiber, which transmits the light to a photodiode outside the magnet. The EMF of the photodiode is measured by a storage oscilloscope. A 1 mm-diameter nozzle, directed at the center of the underside of the droplet (see Fig. 1), is connected to a rubber bulb outside the magnet by a tube. When the bulb is struck on a hard surface, the resulting pulse of air from the nozzle excites several shape oscillation modes simultaneously, with amplitude < 0 . 05 a . Since the focal length of the drop depends on its shape, the intensity of the laser light falling on the photodiode oscillates as the drop vibrates. The temperature of the water was brought to 16 $^{◦}$C in a water bath before it was injected into the potential trap, to match the ambient temperature in the magnet bore. At this temperature, the density of the liquid is ρ = 999 kgm − $^{3}$, its surface tension is T = 73 . 3 mNm − 1 and its kinematic viscosity is ν = 1 . 11 × 10 − 6 m $^{2}$s − 1 [8]. The liquid was injected into the trap using a glass pipette. The volume of liquid injected was determined to better than 1% uncertainty from the difference in the weight of the pipette before and after injection. The liquid was drawn out of the bore using a paper towel, by capillary action, after the experiment. By measuring the difference in weight between the wet and dry paper, we obtained a second measurement of the droplet volume. Using this simple and accurate technique, we were able to determine that the mass loss through evaporation of the drop, during the measurement period (approximately 30-60 minutes), was always less than 2%. Experiments were performed both in air and in dry nitrogen gas (by filling the bore with N$_{2}$ from a pressurized gas cylinder). The air experiments were performed at B$_{0}$ = 16 . 2 T and the nitrogen experiments at 16 . 5 T. The reason for the different B$_{0}$ may be explained by the oxygen content of the air, which, being paramagnetic, buoys up the droplet [9, 10] by an additional force Γ$_{air}$ = −∇ U$_{air}$ . Here, U$_{air}$ = χ$_{air}$B $^{2}$/ (2 µ$_{0}$ρ ) and χ$_{air}$ = +3 . 7 × 10 − 7 is the volume magnetic susceptibility of air (S.I. units). The c ′ 2 component of U + U$_{air}$ is minimized at B$_{0}$ = 16 . 2 T. In nitrogen, the buoyancy force is negligible compared to the diamagnetic force, and c ′ 2 is minimized at 16 . 5 T as shown in Fig. 1. 

## III. RESULTS 

Fig. 2, bottom, shows the oscillations in the photodiode EMF E ( t ) developed by the light refracted through an a = 6 mm droplet; they decay exponentially with a time constant τ ∼ 0 . 1 − 10 s, dependent on a and l , due to the viscosity of the water, i.e. E ( t ) = ∑ l E $_{l}$exp( iω$_{l}$t − 

