Glass Crookes Tube or Cathode Ray Tube. Top is cobalt colored glass on the top side is a knob that ends in a point. The glass tube that makes up the body of the object is cylindrical. Inside, a chunk of a white mineral is held in place by four glass arms. Closer to the bottom of the body is a knob with a wire attached on the inside. The knob is made of cobalt blue glass. The tube stands on a turned wooden base.