Secondary Sources

Reference works include encyclopedias and biographical dictionaries. These are a special kind of secondary source that consolidates and distills general information from many other secondary sources. (For this reason, they are sometimes also called “tertiary” sources.)
You can think of the articles that you find within reference works as “gateway sources” for three reasons: First, they offer an initial broad overview of the topic you are interested in––the background information you need before you can delve deeper. Second, they orient you toward the major people, events, and concepts involved in your historical topics. These are terms you should add to your list of keywords as you continue your research (see the sidebar “Using the Best Keywords” and try the Keyword Brainstorming Tool). Finally, when you find an article in an encyclopedia or biographical dictionary, read it not only for its content, but also for its citations. Look for a “References,” “Works Cited,” or “Bibliography” at the bottom of the article. Because reference works synthesize the work of other scholars, this section can lead you to some of the most reputable secondary sources. Keep in mind that reference works may be scholarly or non-scholarly.
Databases Containing Scholarly Reference Works
The best scholarly reference works for research in the history of science and math include The Complete Dictionary of Scientific Biography and the encyclopedia Science and its Times and they are available through databases that libraries hold subscriptions to. Students at UT Austin should start with:
Gale Ebooks (AKA Gale Virtual Reference Library): http://guides.lib.utexas.edu/az.php?q=Gale%20Virtual%20Reference%20Library 
Cambridge Histories Online: http://guides.lib.utexas.edu/az.php?q=Cambridge%20Histories%20Online
Identify at least two relevant encyclopedia articles using one of the databases. Read the articles and write down any additional keywords for your topic. Most articles will have a bibliography or works cited at the end. Use this to identify some additional secondary sources that look promising for your project. Write down its citation information (see the sidebar “Keeping Track of Your Sources”) so you can find this source in a library.
Make sure you record the title of the article (e.g. “King, Ada Augusta, Countess of Lovelace”) as well as the title of the reference work (i.e. Complete Dictionary of Scientific Biography). Be careful! The title of the reference work is not the same as the name of the database you searched to find it (i.e. Gale Virtual Reference Library). 
A Non-Scholarly Reference
A non-scholarly reference work that you are probably familiar with is Wikipedia. You should certainly use Wikipedia––its articles can help you identify people, events, and concepts. Checking Wikipedia is a very useful early step, but don’t let it be your last or only step! Wikipedia is not scholarly. Anyone can write or change an article. Crowdsourcing means that many articles are of quite good quality, but some are very poor, misleading, or incomplete. Bias also pervades which topics get covered in depth (for example many women scientists are not included or covered in depth, though historians and scientists are working hard to correct those biases). You can only evaluate Wikipedia’s coverage by doing more research.
Following up on the sources it cites in the “References” section at the bottom of the page is a great place to start. Sometimes the “References,” “Further reading,” or “External links” sections of a Wikipedia article can lead to high-quality and scholarly secondary sources. (When you write your lesson plan, you should use and cite only those sources you cross-checked in this way, never just the Wikipedia article.)