should have been obvious. In our opinion, while there may be arguable surface similarity, this was refuted by evidence of the difference in the arc and its effect; and that the similarity begins with the location of the two elements, one being substituted for the other geographically in the hitch arrangement, but that the similarity ends there as the function of the resultant combination was adequately demonstrated to be different by the evidence.
The fact that Reese cannot explain exactly how it happens even after it has been done, as Judge Duffy of this court stated in Canaan Products, Inc. v. Edward Don & Co., id., at 545, is strong proof of the unobviousness of such a combination.
Also, with regard to obviousness, it appears from the evidence that the Reese Patent I hitch would permit lateral as well as forward-backward swinging and that the resistance rather than being of a definite controlling nature would be comparable to that of a gradually subsiding children’s swing. The greater the lack of control of the flexure, of course, the greater would be the likelihood of erratic hitch performance and unpredictable results.
Elkhart, in urging that the combination of parts of Reese’s Patent II claim was obvious from the prior chain-suspension spring bar hitches, credits those skilled in the art with much greater perceptivity than the actual persons in the art, including the engineers and employees of Elkhart, actually exercised or displayed. There was no evidenced conception or production of the claimed hitch in suit until after Reese had placed its patented hitch on the market and had displayed it at the Elkhart Trailer Park. Hindsight is obviously more effective than foresight but we do not place significant weight upon arguments of obviousness based on hindsight.
Judge Kerner of this court has set forth a detailed analysis of the criteria applicable to the determination of the matter of obviousness in Deep Welding, Inc. v. Sciaky Bros., Inc., 417 F.2d 1227, 1232-1233 (7th Cir. 1969). See also, Graham v. John Deere Co. of Kansas City, 383 U.S. 1, 86 S.Ct. 684, 15 L.Ed.2d 545 (1966).
We do not find erroneous the district court’s finding that the combination of functionally cooperating parts to which the claims in suit are directed would not have been obvious at the time the invention was made to a person having ordinary skill in the art.
The findings of fact listed each of the patents and prior art devices which Elk-hart contended invalidated Reese Patent II. Without unduly lengthening this opinion, we merely express satisfaction with the differentiations set forth in the findings of fact to eliminate the anticipation invalidity.
Finally, in reaching the position we do, we note the presumption of validity which attends the grant of the patent which can be overcome only by clear and convincing evidence. Copease Mfg. Co. v. American Photocopy Equipment Co., 298 F.2d 772 (7th Cir. 1961); Helms Products v. Lake Shore Mfg. Co., 227 F.2d 677, 680 (7th Cir. 1955). The presumption of validity is entitled to greater weight when the principal art relied upon by the defendant, as here, has been considered and rejected by the patent office. Hunt v. Armour & Co., 185 F.2d 722,, 726 (7th Cir. 1950); Lewyt Corp. v. Health-Mor, Inc., 181 F. 2d 855, 857 (7th Cir. 1950), cert. denied 340 U.S. 823, 71 S.Ct. 57, 95 L.Ed. 605.
A patented combination which results in a more facile, economical or efficient unit, or which provides results unachieved by prior art structures, cannot be anticipated piecemeal by a showing that the various elements of the invention are individually old. Diamond Rubber Co. v. Consolidated Rubber Tire Co., 220 U.S. 428, 31 S.Ct. 444, 55 L.Ed. 527 (1911); Loom Co. v. Higgins, 105 U.S. 580, 591-592, 26 L.Ed. 1177 (1882); O’Brien v. O’Brien, 202 F.2d 254, 255