When, in the course of a few years, the new school of physics in Berlin was formed, he entered on a correspondence with its representatives—with E. Brücke, E. Du Bois-Reymond, and H. Helmholtz. Ludwig's first opportunity of meeting these somewhat younger friends was in 1847, when he made a short visit to Berlin. It was then that he also made the acquaintance of E. H. Weber and A. Volkmann. He seems to have led Volkmann to the use of his recently invented kymographion, for, as is known by common report, they experimented together for a time.
In his manner of investigating, Ludwig was all his life a most acute analyzer, seeking with the utmost care to separate every vital process into its various branches, and to determine the conditions of its manifestations. In this work he always attached great importance to the quantitative determination of all the factors of the problem. This manner of work of course often resulted in the questions that he had investigated seeming further from a satisfactory solution than before he had begun; Ludwig, however, never regarded any line of research as definitely closed, but years later returned again and again to work on the problems he had undertaken to solve, and continued his researches with the help of his added knowledge and experience. Herein lay one of the most interesting sides of his richly endowed nature; in his search for the truth he never faltered, but with untiring energy continually attacked the problem with new weapons.
Ludwig's mode of scientific work was entirely opposite to E. H. Weber's. Weber possessed the gift of artistic intuition. He absorbed himself in his problems until he believed that he had mastered the main substance of the matter, after which he was able in a few clear strokes to draw an illustration of oftentimes wonderful simplicity. Weber's scheme of the circulation, constructed by the insignificant means of a piece of intestine and a few lamp chimneys, solved with one stroke, convincing even to beginners, some of the most abstruse problems of the theory of the circulation, and even the complicated technique of later physiology has not been able to dispense with it. The first one to recognize this was Ludwig himself; in fact, he went so far as to consider Weber's discoveries of greater importance even than Harvey's discovery of the circulation of the blood. Intuitive natures, such as Weber's, may make particularly clear teachers. The artistic perception, however, which is their most valuable quality, can not be transferred to others, and thus we seldom find them as founders of any school of science. Thus Weber, if we do not include his personally congenial friends, never in all his long career attracted scientific pupils. Ludwig, on the other hand, made
works on the circulation of the blood (1832), and Johann Müller's investigations on the formation of the voice.