The attainment of mechanical invisibility reached a state of perfection in the year 2000 sufficient to make it practical for many uses. For a century this result had been sought. It came, about the year 2000, not as a single startling discovery, but as the culmination of the patient labor of many men during many years. The popular mind has always considered that science advances by a series of "great scientific discoveries"; "unprecedented"; "revolutionary." That is not so. Each step in the progress of scientific achievement is built most carefully upon the one beneath it. And generally the "revolutionary, unprecedented discovery" has very little of itself that is new; rather it is a new combination of older, perhaps seemingly impractical knowledge. Every scientific theory, every device, is the offspring from a large and varied family tree of many scientific ancestors, each of whom in his day was a remarkable personage. Thus it is, with the principles of mechanical invisibility. I deal here with the famous X-flyers. The operation of the plane itself is immaterial; its motors; its wing-spread surfaces; its aerial controls. I am concerned only with the scientific principles underlying its power of invisibility. Three scientific factors are involved: First, the process known as de-electroniration; second, the theories of color absorption; third, the material, inevitable deflection (bending) of light rays when passing through a magnetic field. I take each of the three in order. The forerunners of de-electroniration were the Martel effects--the experiments of Charles Martel, in Paris, in 1937. A new electric current, of a different character--now called the oscillating current as distinct from the alternating and direct--was developed. Metallic plates were electro-magnetized to produce an enveloping magnetic field of somewhat a different character from any field formerly known. Dr. Norton Grenfell followed this in 1946 by using the Martel oscillating current to obtain a reverse effect. A similar disturbance of electrode balance. But not a surcharge. An exhaustion. An anti-electrical state, instead of a state of magnetism. A metallic mass so treated--and with a constant flow of oscillating current holding its subnormal electronic balance--was then said to be de-electronired.