In Napoleon's case, it led him to the unforgivable military crime; that of underestimating the enemy. His imagination, by presenting a magnified image of himself, presented relatively dwarfed images of his antagonists. The very faculty (imagination) which started Napoleon on his great successes, started him now on his great reverses. The actual beginning of these was in his carelessly planned campaign in Russia. His invention seems to have failed him both in planning the campaign and in meeting situations afterwards; because his imagination failed to picture each situation to him exactly as it was. But the Russian campaign did not wholly ruin him. Even after that, even after Elba, situations were sometimes presented to him, such that (although Trafalgar had prevented him from achieving European domination), yet, if he had been able to see them as clearly as he had seen situations in his unspoiled days, he might, at least have saved himself from ruin. But his imagination had become impaired and therefore his powers of invention also. Napoleon as general, and Nelson as admiral were what we may term "opportunistic inventors," who made inventions for meeting transient situations with success, as distinguished from inventors like Newton and Watt, who made permanent contributions to the welfare of mankind. Napoleon as statesman, however, made contributions of a permanent character. A supremely valuable contribution of this kind was the stethoscope, which was invented about 1819 by Dr. Laennec in Paris, and by means of which the science and art of diagnosis were given an amazing impetus almost instantly. Possibly one cannot find in the whole history of modern invention any instrument so small and so inexpensive that has been so widely and definitely useful. A painful interest hangs to it in the fact that by means of his own invention, Laennec discovered that he himself was dying of tuberculosis of the lungs.