PMC

A. Guide for directing transfer tube into liquid helium Dewar.
B. Metal bellows to permit differential expansion between the central tube and the supporting thermometer block well.
C. Exit for the vacuum line and electrical leads to the thermometers, the thermocouples, and the heater on the copper thermometer block.
D. Supporting shelf.
E. Demountable “O” ring seal to the well around the thermometer block.
F. Well around the thermometer block.
G. Central tube for supporting the thermometer block.
H. Seal for the electrical leads from the vacuum can that surrounds the shield and lower portion of the thermometer block well.
I. Line from vacuum can “O”.
J. Demountable “O” ring seal to the liquid helium Dewar.
K. Glass stopcock to permit reevacuation of liquid helium Dewar.
L. Line for pumping the space within the liquid helium Dewar.
M. Liquid helium Dewar.
N. Thermal tie-down for lead wires.
O. Vacuum can that surrounds the lower portion of the thermometer block well and the thermal shield.
P. Copper sleeve on vacuum can to maintain uniform temperature when liquid helium level is low.
Q. Thermal tie-down for leads similar to N with a heater and five-junction Chromel-P/constantan thermocouple for temperature control.
R. Copper ring on the thermometer block well with temperature control components similar to Q.
S. Heavy copper shield with temperature control components similar to Q.
T. Thermometer lead terminal block of anodized aluminum.
U. Capsule type platinum resistance thermometers thermally attached to copper block with vacuum grease.
V. Copper thermometer block with holes for six thermometers.
W. Location of thermocouple junctions placed on shield.
X. Reentrant “thumb” in the bottom of well. “Thumb” contains reference junctions for thermocouples on R and S.
Y. Heavy copper tail on vacuum can to reach liquid helium at a low level.

Experimental setup for the visual inspection (A): the LCMRV thermometer was placed within a water bath with PRT placed on either side of the LCMRV thermometer. Using the experimental setup in (A), we observe the visual transition of the target 17°C cell of the LCMRV thermometer from the cholesteric crystalline state (B), which appears iridescent, to the isotropic state (C), which appears clear or colorless. Finally, (D) shows the start of the transition of the target 18°C cell, with a slight color shift from bright white to bright green. For MRI experiments (E), the LCMRV thermometer was placed within an enclosed water bath surrounded by an outer shell containing Fluorinert FC-40 (TMC Industries, Waconia, MN). A fiberoptic thermometer was placed near the LCMRV thermometer. LC, liquid crystal; LCMRV, LC MR-visible; PRT, platinum resistance thermometers

A comparison with T₅₈ of temperatures derived from isotherm measurements, gas thermometry and the acoustical interferometer.
⦶ ⦵ ◯-Schmidt and Keesom [9] (gas thermometer. 1937).
●-Kistemaker [10] (gas thermometer, 1946).
×-Kistemaker [10] isotherms, 1946).
△-Berman and Swenson [11 1 (gas thermometer, 1954).
□-Keller [12] (helium 4 isotherms, 1955).
■-Keller [12] (helium 3 isotherms, 1955).
▲-Preliminary results [4.5] (velocity of sound in helium 4 gas. acoustical in interferometer. 1962).
◆-Present work (isotherms determined by the NBS acoustical thermometer).

Effect of immersion in zinc cell at the freezing point, NBS thermometers, plotted from the data in . “Station” is the vertical location of the thermometer in the cell well; it represents the elevation of the thermometer, in cm, above full immersion. The thermometer is fully immersed and resting on the bottom of the cell well at station 0. Δ t is the temperature equivalent of the difference in thermometer resistance, measured when the thermometer is fully immersed at station 0 and when it is elevated to the indicated station. The straight line represents the expected temperature gradient due to the hydrostatic pressure of the liquid zinc.