23 in front of the second displacer 25 by the motor 45 the mechanical linkage 47 and the magnetic linkages 49a and b this produces cold at the top of the first cylindrical working vessel 13 with excess heat being dissipated from the cooling fins 37 and 39 to explain this result it is noted that the first cylindrical working vessel 13 is very similar to the cylinder of a small stirling cycle refrigerator the only thing that is missing is a piston which in the stirling cycle operates in the same cylinder but below the displacer the task of the piston in a stirling cycle device is to produce a variable pressure having a suitable phase difference with the variations of the cold expansion volumes in the connecting conduit 21 however no matter how a given pressure variation in the expansion volume is produced the same cold production will result in the vuilleumier cycle apparatus described herein the pressure variations in the cold volume are not produced by the motion of a compression piston but rather by the motion of the second displacer 25 as follows if the second displacer 25 is 34 down 34 much of the helium is in the hot upper space 33 the average helium temperature will be high and.