Hello, I have read an interesting paper from the Proceedings of the American Philosophical Society about the use of the V-2 rocket at White Sands, New Mexico for high-altitude research. In it the different gauges for atmospheric pressure measurement were mentioned, as well as the difficulty to cover a pressure range of 108 mmHg. The article then went on by explaining that the pressure is first measured by a bellows gauge, then by a Pirani gauge. For the lowest pressures either ionization or "Philips" Gauges would be used. I would like to know what a Philips Gauge is, because I did not find information on that on the Internet. Thank you!