in patent law, the principle of a machine is the particular means of producing a given result by a mechanical contrivance. Parker v. Sliics, 5 McLean, 44, 03, Fed. Cas. No. 10,749. The principle of a machine means the modus operandi, or that which applies, modifies, or combines mechanical powers to produce a certain result; and, so far, a principle, if new in its application to a useful purpose, may be patentable. See Barrett v. Hall, 1 Mason, 470, Fed. Cas. No. 1,047.