If you are interested in a specific technology, the Groundbreaking Scientific Experiments, Inventions and Discoveries series can be an excellent starting point!
The following links will take you to large digital collections of subject encyclopedias. The Gale Virtual Reference Library is an especially good place to start for STS courses, as it includes the Mcgraw-Hill Dictionary of Science & Technology and the Dictionary of Scientific Biography.
You'll find these print sources in the reference section on the main floor or in the main stacks! As you use these and other reference sources, keep these tips in mind: