November 8, 1895 is the date when Wilhelm Röntgen discovered the effects of X-rays, and today Google is celebrating the 115th anniversary of this day with a special Doodle.
The logo is composed of an X-ray of several bones and some other objects forming the letters. It contains a nod to one of Google's own April fools jokes: the small g is made up of bones of a pigeon, referring to PigeonRank, a parody on the PageRank system in which domesticated pigeons determine the order of search results. Google's vice-president of search products, Marissa Mayer, confirms the reference on her Twitter account.
Röntgen dedicated much of his further life to investigating the mysterious phenomenon he discovered, which he appropriately named X-rays (still called Röntgens in many parts of the world), and in 1901 was awarded the first Nobel Prize in Physics.
For more information on Wilhelm Röntgen and his discovery of X-rays, see the Wikipedia article linked below.
More information from Wikipedia: Wilhelm Röntgen