The time for the temperature in a vapour pressure system to equilibrate with the surrounding main liquid helium bath at 4·2°K, when ⁴He condensed in the copper bulb, was found to be unexpectedly long. The vapour pressure system consisted of a copper bulb, volume 2 cm³, connected to a mercury manometer by a vacuum jacketed thin walled stainless-steel tube of 5 mm outer diameter. A germanium thermometer was mounted inside the bulb to record the temperature changes when helium was condensed or when, thereafter, small amounts of gas were admitted or extracted from the system. It is suggested that the relaxation time, from the beginning of the admission of helium till thermal equilibrium is restored, could be proportional to the diameter and the length of the jacketed vapour pressure tube.