By Earl Hunsinger Remember that picture of the periodic table of elements that was in the back of your high school or college chemistry book? Or the table of trigonometric values that could be found in your math book? Their equivalents can be found online, along with an abundance of other reference material. Numerous color versions of the periodic table of elements can be found simply by searching. Often, these are interactive. A good example of this is the table provided by the Particle Data Group, which publishes the biannual 1,200-page book, Review of Particle Physics. The 'Atomic and Nuclear Properties' page of their website allows a user to click on many of the elements in the periodic table, to obtain more information. This often includes, not only the atomic number and mass, but also values for the minimum ionization, nuclear collision length, nuclear interaction length, pion collision length, pion interaction length, radiation length, critical energy, Moliere radius, plasma energy, muon critical energy, and the melting and boiling points at one atmosphere. Drop down boxes allow you to find some of the same information for dozens of inorganic compounds, simple organic compounds, polymers, mixtures, and biological materials. The website 'web elements', which can be reached from the site mentioned above, contains a brief description of each element, including how it is isolated (for many elements). Berkeley laboratory maintains a website with information on the periodic table of isotopes. Other links that can be found on the Particle Data Group's website take you to a variety of other tables and calculators, including those that show the X-ray absorption and other optical properties for various materials (for 30eV to 30 keg), and the stopping power and range tables for electrons, protons, and alpha particles in selected materials. An Internet search for physical constants will bring up many good references for these. For example, on the website maintained by the National Institute of Standards and Technology, you'll find lists for universal constants, electromagnetic constants, atomic and nuclear constants, and physico-chemical constants. You can also find the correlation coefficient between any pair of constants and data from the least-squares adjustment of the values of the constants. In the same way, lists of mathematical constants and explanations for how they are derived are readily available. Other websites provide mathematical tables. These include everything from simple multiplication tables and fraction-decimal conversion tables to tables of integrals and derivatives. Information on advanced topics, such as statistical distributions and Fourier transforms, is also available. The website 'eformulae' provides reference information for the mathematics, physics, chemistry, and engineering fields. Here, you'll not only find tables, such as for drill and thread sizes, but also a wealth of formulas. Other scientific and technical references to be found include metric conversion tables, ASCII character codes, HTML color codes, and so on. You may still have the math and science textbooks that you used in school, with their colorful tables in the back. For that matter, you may still be in school and using those tables on a daily basis. Yet, even if you've given them up for lack of shelf space, or they aren't currently accessible, there's no need to worry the next time you need the information. The Internet contains the same reference material. More than that, it often presents the information in a way that just isn't possible with a more traditional format.