A new instrumental method for measuring the physical properties of a liquid has been developed. The instrument, called a capacitive drop tensiometer (CDT), is based on the drop volume principle in combination with a capacitive transducer. A delivery head with a specialized wetting design was constructed for forming drops. The capacitive transducer uses the delivery head as one of its plates and a cylindrical ring plate, which surrounds the delivery head and the space occupied by the drop that is formed, as another. Excellent linearity is achieved by optimizing the design, with an accuracy of drop volume measurement of approximately . The system is suitable for measuring both drops in equilibrium and those in the process of growing. Its capability of real-time measurement makes it particularly useful for volatile liquids, in which instance the measurement of drop volume using a flowmeter or a pump is no longer reliable. The CDT can also be used to determine concentration. It was found that the concentration curve is linear for aqueous glycerol solutions although not so for aqueous ethanol solutions. The CDT's ability to measure surface tension was also explored and experimental results are presented here.

We present the results of an investigation of the speed of a radially infalling test particle crossing the event horizon of a black hole within a Schwarzschild spacetime. One finds that the speed as measured by a special class of observers, at rest outside the horizon and static inside the horizon, increases when the test particle approaches the horizon but decreases inside the horizon. The corresponding situation regarding black holes possessing both outer and inner horizons is also briefly discussed.