In the mean time, during the progress of the investigations on the dynamo, word had gone out to the world that Edison expected to invent a generator of greater efficiency than any that existed at the time. Again he was assailed and ridiculed by the technical press, for had not the foremost electricians and physicists of Europe and America worked for years on the production of dynamos and arc lamps as they then existed? Even though this young man at Menlo Park had done some wonderful things for telegraphy and telephony; even if he had recorded and reproduced human speech, he had his limitations, and could not upset the settled dictum of science that the internal resistance must equal the external resistance. Such was the trend of public opinion at the time, but "after Mr. Kruesi had finished the first practical dynamo, and after Mr. Upton had tested it thoroughly and verified his figures and results several times--for he also was surprised--Edison was able to tell the world that he had made a generator giving an efficiency of 90 per cent." Ninety per cent. as against 40 per cent. was a mighty hit, and the world would not believe it. Criticism and argument were again at their height, while Upton, as Edison's duellist, was kept busy replying to private and public challenges of the fact.... "The tremendous progress of the world in the last quarter of a century, owing to the revolution caused by the all-conquering march of 'Heavy Current Engineering,' is the outcome of Edison's work at Menlo Park that raised the efficiency of the dynamo from 40 per cent. to 90 per cent."