Considered one of the most scholarly encyclopedias published, the 1911 Encyclopedia Britannica is available free online.
Topics are covered in much more depth than we are used to seeing in an encyclopedia. Over 1500 authors contributed to the more than 40 million words.
The bibliographies at the end of articles are also helpful for continuing research.
Great tool for developing an independent researcher!
Also available on Kindle:
7 Ways to Develop an Independent Researcher
Important skill to develop!
10 Ways to Use Notebooking: #9 Research & Projects
A place to hold and options for organizing a research project!