Abstract: An optical measuring device includes a sensor which emits light flashes toward a subject of detection with a light emitting element which is supplied with electric power from a rechargeable battery for a certain duration at certain intervals and receives reflected light from the subject with a light sensitive element. A subtractor subtracts a d.c. component from a sensed signal provided by the light sensitive element, thereby extracting a variation component. The subtractor has its output signal amplified with an amplifier, with the output thereof being A/D-converted with an A/D converter.

Abstract: A glass for a data storage medium substrate, which consists essentially of the following components as represented by mol %: SiO2 60 to 72, Al2O3  2 to 9 MgO  3 to 9, CaO  2 to 10, SrO  0 to 15, ZnO  0 to 4, TiO2  0 to 8, ZrO2  0 to 4, Li2O  1 to 12, Na2O  0 to 8, K2O  0 to 5, Y2O3  0 to 5, La2O3  0 to 5, and Li2O + Na2O + K2O  4 to 15, and which has a Young's modulus of at least 85 GPa.

Abstract: A glass for substrate, which consists, as represented by mass percentage, essentially of: 1 SiO2 40 to 59%, Al2O3  5 to 20%, B2O3  0 to 8%, MgO  0 to 10%, CaO  0 to 12%, SrO  2 to 20%, BaO  0 to 2%, ZnO  0 to 4%, Li2O  0 to 2%, Na2O  0 to 10%, K2O  0 to 12%, TiO2  0 to 10%, and ZrO2  0 to 5%,

Abstract: A glass for a substrate, having an average thermal expansion coefficient in the range of from 60×10−7 to 75×10−7/° C. at 50 to 350° C., which consists essentially of the following composition expressed by wt %: wt % SiO2 more than 62 to 74, Al2O3  1 to 15, MgO  0 to 9, CaO  0 to 14, Na2O  0 to 12, K2O  0 to 13, SiO2 + Al2O3 72 to 82, MgO + CaO  5 to 24, Na2O + K2O  1 to 15, MgO + CaO + Na2O + K2O 18 to 28.

Abstract: A glass for a substrate consisting essentially of: SiO2 45 to 65 wt %, Al2O3 6 to 20 wt %, B2O3 0.5 to 6 wt %, MgO 2 to 5 wt %, CaO 1 to 10 wt %, SrO 0 to 6.5 wt %, BaO 0 to 2 wt %, MgO + CaO + SrO + BaO 10 to 17 wt %, ZrO2 0 to 7 wt %, and Na2O + K2O 7 to 15 wt %.