E. H. Risley, for appellant.

Geo. T. Spencer, for appellee.

Mr. Justice WHITE delivered the opinion of the court.

The sole question in this case is whether the appliance to which the plaintiff in errot claims the rights of a patentee under the grant of letters patent No. 134,978, bearing date January 21, 1873, issued to his assignor, involves invention, or is simply a manifestation of mechanical skill.

There is no doubt that in this, as in all similar cases, the letters patent are prima facie evidence that the device was patentable. Sitll, we are always required, with this presumption in mind, to examine the question of invention vel non upon its merits in each particular case. In the present instance the letters patent state the device to be an improvement in gratings for sewer inlets, and describe it as follows: [156 U.S. 342, 343] My improvement consists in the employment of a device to elevate the grating above the opening which it covers a short distance, so that it will not become obstructed by small sticks, straws, leaves, and other small rubbish not large enou