Sentence:  Several germanium resistors have been thermally cycled from 300 to 4.2 * * f and their resistances have been found to be reproducible within 1 3 millidegree when temperatures were derived from a vapor pressure thermometer whose tubing is jacketed through most of the liquid <WSD>helium</WSD> . 
Meaning of the word marked with <WSD> tags:  a very light colorless element that is one of the six inert gasses; the most difficult gas to liquefy; occurs in economically extractable amounts in certain natural gases (as those found in Texas and Kansas)