X-ray machine – The X-ray machine was an invention which had its public debut at the 1904 World 's Fair . X-rays were first discovered in November 1895 by a German scientist , Wilhelm Conrad Röntgen , who at the time was studying the phenomena accompanying the passage of an electric current through a gas of extremely low pressure . After Rontgen 's discovery , he took an x-ray of his wife 's hand , showing the bones and her fingers along with her wedding ring , and sent it to several of his scientist colleagues . One of the scientists that learned of the discovery was Thomas Edison and he soon began to experiment with his own x-ray machine with his assistant Clarence Dally . In 1901 , Dally brought a test version of the x-ray machine to the 1901 World 's Fair , but failed to test the machine when President McKinley was assassinated . For the 1904 World 's Fair , the x-ray machine was perfected and successfully shown to the public . X-rays are now commonplace in hospitals and airports
President McKinley was assassinated
Assassination of William McKinley
Louisiana Purchase Exposition