itself, but since the grant by the government is for a definitely
prescribed term of years, as each of those years goes by there passes
with it some portion of the value attaching to the exclusive enjoyment
of the right for the prescribed period. In this country a mechanical
patent is granted for a term of seventeen years, after which the
patented device or process becomes common or public property. The
period allowed for patents covering designs is three and one-half,
seven, or fourteen years, depending on the application. Thus, simply
through the lapse of time the value of the right diminishes.