In the mid 1800's, Mendeleev put all known atoms into a table based on their weights and how they behaved chemically. Here's an early version of his table:

When Mendeleev looked at his table, it was clear some elements were missing. Some elements were yet to be discovered.

In 1868, a scientist named Lockyer pointed his spectrograph at the Sun, and he saw the spectral lines from Hydrogen, but there were also spectral lines from an element he didn't recognize. He called the unknown element Helium. Much later, in 1895, helium was found on the Earth.

Now, you will perform the same type of experiment. Just as in the previous level of the game, we'll show you the spectral lines of two elements at the same time. Your job is to tell us which two elements we've mixed together.

BUT, there's a twist. In this final level of our game, let's pretend we're living back in 1869 and we only know Medeleev's elements. When you try to match the target spectra, sometimes, you'll find that you can't do it -- a needed element is missing. You will need to recognize when you are missing an element required to match the spectrum. If you get four of these puzzles right, you'll complete this level and earn 4 clams salary.

Onward...to the game!