 Complete the following phrase:  Rieussec was again present at the 1844 exposition. That year, the jury was delighted to acknowledge how prolific Mr. Rieussecs invention has been in terms of useful applications, and hastened to do him justice by awarding him a silver medal. In 1851, he was in London exhibiting in the Crystal Palace. Once again, his products, attracted notice. The ingenuity of the mechanical combinations used by Mr. Rieussec to conveniently and reliably obtain a result so valuable to experimenters so impressed the London jury that the creator of this mechanism was uimously found worthy of the first prize, and - to the great regret of all the judges - was deprived of it only by the clause in the rules stipulating that the highest award could not be given to an invention more than twenty years old. Which, however, did not prevent him from being awarded a prize medal. The 