MEDIUM, in philosophy, that space or region through which a body in motion passes to any point: thus ether is supposed to be the medium through which the heavenly bodies move; air, the medium wherein bodies move near our earth; water, the medium wherein fishes live and move; and glass is also a medium of light, as it affords it a free passage. That density or consistency in the parts of the medium, whereby the motion of bodies in it is retarded, is called the resistance of the medium; which, together with the force of gravity, is the cause of the cessation of the motion of projectiles.
Subtile or Ethereal MEDIUM. See ETHER, ELECTRICITY, FIRE, &c.