Abstract: A thermal-optical converter which comprises an aqueous solution containing a non-ionic compound with a functional group, a closed vessel for containing the solution and a transparent window fitted to at least one part of the closed vessel which allows the solution to be visible. Because the aqueous solution is transparent at low temperatures and opaque at elevated temperatures, the thermal-optical converter can effect reversible optical changes in accordance with changes in the temperature of the solution.

Abstract: Provided is a liquid crystal device comprising a lyotropic-type cholesteric liquid crystal and an enclosure surrounding the liquid crystal, at least a part of which enclosure is transparent, so that the color of the liquid crystal, varying depending upon the change of temperature, is viewable therethrough. The liquid crystal is a concentrated solution having a concentration of approximately 50 to 85 wt.% of a cellulose derivative in water or an organic solvent. The cellulose derivative has an average polymerization degree of 30 to 600 and a chemical structure such that the --OH groups in the cellulose molecule are at least partially substituted with at least one radical of the following formula to the extent that the mole number (M.S.) of a hydroxyalkylating agent bonded with cellulose, per anhydro glucose unit of the cellulose molecule, is 2.0 to 10.0 at average:-- O -- X -- CHR.sub.1 -- CHR.sub.2 -- O ].sub.m Hwhere X is direct bond or --CO--; and, when X is direct bond, R.sub.1 is H or --CH.sub.3, and R.