The low temperature characteristics of some commercially manufactured carbon‐composition thermometers are discussed. A semiempirical equation relating resistance and temperature and having three adjustable constants is given. Temperatures calculated by this equation are within ±0.5 percent of the measured temperatures from 2° to 20° Kelvin. Temperature values are reproducible within about ±0.1 percent from run to run, making possible the interpolation of temperatures from 4° to 10° Kelvin on the basis of calibrations in liquid helium and hydrogen only. Thermometric sensitivity is such that by measuring resistance to one part in 5000 it is possible to detect temperature changes smaller than 0.01° at 20° and smaller than 0.0001° at 2° Kelvin. The variation of resistance with measuring current can be interpreted as Joule heating of the resistor by the measuring current. Magnetic field sensitivity is small, the change in resistance with field being proportional to H2. Equations are given which permit an estim...
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