Some of the lectures were almost easy for me—for instance, those on mathematics. I have always been able to perceive with ease and pleasure relations of geometrical figures and of planes; so that it seemed inexplicable to me that every farmer should not be equally capable of understanding them. This I had said before to my brother, who tried to give me an explanation; but I did not yet grasp it. I had expected I don't know exactly what, but certainly something higher, something grandiose; very likely I had expected something with more life in it. The mathematical course, therefore, at first seemed to me unimportant; but later on I found that I, also, could not follow every detail. However, I did not think much of this, because I readily understood the general meaning, and I said to myself that particular cases would not cause me any mental fatigue if I found it necessary to learn them.
The lectures of my excellent teacher were not so useful to me as they might have been, if I could have seen in the course of instruction and in its progress somewhat more of necessary connection and less of arbitrary arrangement. This want of necessary connection was the reason of the immediate dislike I always took to every course of instruction. I felt it even in pure mathematics, still more was it the case in applied mathematics, and most of all in experimental physics. Here it seemed to me as if everything were arranged in arbitrary series, so that from the very first I found this study a fatigue. The experiments failed to arrest my attention. I desired and sought after some inner connection between the phenomena, deduced from and explained by some simple root principles. But that was the very point withheld from me. Mathematical demonstrations came like halting messengers; they only became clear to the mind's eye when the truth to be demonstrated lay before me already in all its living strength. On the other hand, my attention was riveted by the study of gravitation, of force, of weight, which were living things to me, because of their evident relation to actual facts.
In mechanics (natural philosophy) I could not understand why so many of the so-called "mechanical powers" were assumed, and why several of them were not reduced to cases of the inclined plane.
In mineralogy my previous education had left many gaps unfilled, especially as regards the powers of observation. I was fond of mineral specimens, and gave myself much trouble to comprehend their several properties; but in consequence of my defective preparation I found insuperable difficulties in my way, and perceived thereby that neglect is neither quickly nor lightly to be repaired. The most assiduous practice in observation failed to make my sight so quick and so accurate as it ought to have been for my purpose. At that time I failed to apprehend the fact of my deficient quickness of sight; it ought to have taught me much, but I was not prepared to learn the lesson.
Chemistry fascinated me. The excellent teacher (Göttling) always demonstrated the true connection of the phenomena under consideration; and the theory of chemical affinity took strong hold upon me.
Note-taking at these lectures was a thing I never thought of doing; for that which I understood forthwith became a part of me, and that which I failed to understand seemed to me not worth writing down. I have often felt sorry for it since. But as regards this point, I have always had through my whole life the perfectly clear conviction that when I had mastered a whole subject in its intimate relations I could go back upon, and then understand, details which at the time of hearing had been unintelligible to me.
In botany I had a clear-sighted, kind-hearted teacher (Batsch). His natural system of botany[20] gave me great satisfaction, although I had always a painful perception of how much still remained for him to classify. However, my view of Nature as one whole became by his means substantially clearer, and my love for the observation of Nature in detail became more animated. I shall always think of him with gratitude. He was also my teacher in natural history. Two principles that he enunciated seized upon me with special force, and seemed to me valid. The first was the conception of the mutual relationship of all animals, extending like a network in all directions; and the second was that the skeleton or bony framework of fishes, birds, and men was one and the same in plan, and that the skeleton of man should be considered as the fundamental type which Nature strove to produce even in the lower forms of creation.[21] I was always highly delighted with his expositions, for they suggested ideas to me which bore fruit both in my intelligence and in my emotional nature. Invariably, whenever I grasped the inter-connection and unity of phenomena, I felt the longings of my spirit and of my soul were fulfilled.
I easily understood the other courses I attended, and was able to take a comprehensive glance over the subjects of which they treated. I had seen building going on, and had myself assisted in building, in planting, etc.; here, therefore, I could take notes, and write complete and satisfactory memoranda of the lectures.
My stay in Jena had taught me much; by no means so much as it ought to have taught me, but yet I had won for myself a standpoint, both subjective and objective. I could already perceive unity in diversity, the correlation of forces, the interconnection of all living things, life in matter, and the principles of physics and biology.
One thing more I have to bring forward from this period. Up till now my life had met with no sympathetic recognition other than the esteem which I had enjoyed of the country physician during my apprenticeship—he who encouraged me to study natural science, and smoothed away for me many a difficulty. But now such sympathy was destined to offer itself as a means of education and improvement. For there were in Jena just then two scientific associations, one for natural history and botany, the other for mineralogy, as it was then called. Many of the young students, who had shown living interest and done active work in natural science, were invited to become members by the President, and this elevating pleasure was also offered to me. At the moment I certainly possessed few qualifications for membership; the most I could say was that my faculty for arranging and classifying might be made of some use in the Natural History Society, and this, indeed, actually came to pass. Although my admission to this society had no great effect upon my later life, because it was dissolved at the death of its founder, and I did not keep up my acquaintance with the other members afterwards, yet it awakened that yearning towards higher scientific knowledge which now began to make itself forcibly felt within me.