that it employs an ordinary LED as a twilight detector and no external optics beyond the epoxy lens in which the LED chip is encapsulated. Instead of a multi-stage amplifier, he uses a single operational amplifier with a feedback resistor of from 10 to 20 gigohms to provide a gain of 10 to 20 billion. Since 2013, Mims has used several LED twilight photometers to detect layers of smoke and dust in the troposphere and volcanic aerosols in the stratosphere. Sulfur dioxide from the 21-23 June 2019 volcanic eruption of Raikoke reached the stratosphere and covered much of the northern hemisphere with a veil of sulfuric acid aerosols. Mims’ twilight photometry from Central Texas and lidar measurements from Hawaii indicated that the elevation of the densest portion of the veil reached 25 km and was typically 16-20 km. Furthering science Forrest Mims has participated in forming a science-focused team in his three children. Daughter Sarah used kite-held smoke-and-spore sampling to keep the collection high away from local ground and airs while verifying the remote conditioning of the wind. Forrest had participated in setting up a stand on the ground for sampling the winds, but Sarah wanted to remove local-air-and-ground influences. References Sources Books List of books, booklets, manuals by Forrest Mims. Radio Shack Introduction to Electronics (1972) Introduction to Transistors (1972) Transistor Projects, Volume 1 (1973) Transistor Projects, Volume 2 (1974) Transistor Projects, Volume 3 (1975) Transistor Projects, Volume 4 (1976) Integrated Circuit Projects, Volume 1 (1973) Integrated Circuit Projects, Volume 2 (1974) Integrated Circuit Projects, Volume 3 (1975) Integrated Circuit Projects, Volume 4 (1975) Integrated Circuit Projects, Volume 5 (1976) Integrated Circuit Projects, Volume 6 (1977) Electronics Music Projects (1977) Computer Circuits for Experimenters (1974) Semiconductor Projects, Volume 1 (1975) Semiconductor Projects, Volume 2 (1976) Security for Your Home (1974) Optoelectronic Projects (1975) Radio Shack Introduces the World of Computing (1977) Understanding Digital Computers (1979) Engineer's Notebook 1 (1979) Engineer's Notebook 2 (1982) Beginner's Guide to Personal Computers (1981) Getting Started in Electronics (1983) Engineer's Mini-Notebook: 555 Timer IC Projects (1984) * Engineer's Mini-Notebook: Op-Amps (1985) Engineer's Mini-Notebook: Optoelectronics (1985) Engineer's Mini-Notebook: Basic Semiconductor Circuits (1986) Engineer's Mini-Notebook: Digital Logic Circuits (1985) Engineer's Mini-Notebook: Formulas, Tables & Basic Circuits (1988) Engineer's Mini-Notebook: Schematic Symbols, Design and Testing (1988) Engineer's Mini-Notebook: Communication Projects (1985) Engineer's Mini-Notebook: Science Projects (1990) Engineer's Mini-Notebook: Environmental Projects (1995) Engineer's Mini-Notebook: Sensor Projects (1996) Engineer's