26 TESTING, DEMONSTRATING AND MEASURING APPARATUS FOR TEACHING PHYSICS, CHEMISTRY AND LIKE SCIENCES, AND TESTING AND MEASURING APPARATUS FOR LABORATORY USE-NAMELY, VACUUM AND PRESSURE GAUGES, [ MANOMETERS, HYGROMETERS, THERMOMETERS, (( ACOUSTIC, OPTIC AND )) ELECTRICAL MEASURING INSTRUMENTS, ] (( VACUUM AND HIGH-VACUUM MEASURING INSTRUMENTS, [ VAN DE GRAAF ACCELERATORS AND LINEAR ACCELERATORS; NUCLEAR LABORATORY APPARATUSES; ] CRYOGENIC UNITS AND PARTS THEREOF ))