Neu-Schönefeld, the entry in my diary reads: "Fleischer as bright as ever." But in 1886, he was compelled to avail himself of the permission granted him, on the occasion of his jubilee celebration, to omit the lectures of the summer session, and the physician's orders were constantly limiting the amount of work he did. When again I visited him at Leip zig in October 7, 1887, I felt that I should have to bid him an eternal farewell. In spite of his increasing debility he began a course of lectures for the winter session, and continued them until November 17. But on November 18 he took to his bed, never again to leave it. He bore the pain entailed by his disease with admirable patience; no complaint ever crossed his lips, until on February 10, 1888, a short while before completing his eighty-seventh year, death released him from his suffering. The prominent features of Fleischer's character were truthfulness, conscientiousness, unselfishness, and punctuality. I was never able to decide how much he owed to nature, how much to the strict self-discipline exercised in early years. But whatever he had acquired by habit had come to be a part of his being. He became indignant nay wrathful, the kindliness that marked his features and sprung from good nature in the best meaning of the word, seemed to leave him,-when he met with falsehood, carelessness, or lack of punctuality. As long as there were no evidences of want of truth on the part of others, he was unsuspicious, sometimes too much so; but whoever shocked his delicate sense of justice, had good cause to fear his anger. Yet there was not a trace of dogmatism in his nature. He may in some instances have chanced to form an incorrect judgment of certain people, but he took the first opportunity to change it most willingly in their favor, unless weighty reasons existed for the contrary. All that he thought and did was characterized by objectivity, pure and simple. In scientific debates he demanded that his conclusions be tested impartially, and on the other hand he accepted instruction from the youngest of his pupils, if he had chanced to find something that had escaped the notice of "the sheikh." His polemics were never of a personal nature except when Ewald accused him, in a manner that even now impairs the reputation of this great man of "being actuated by sordid impulses in science." In a published "statement addressed to Prof. Dr. Ewald of Göttingen," he expresses in plain, though moderate terms, his just indignation. His misunderstanding with Dozy, whom Fleischer had unintentionally offended, was cleared up in a way that reflects credit upon both scholars. He was conscious of his abilities and his achievements, but never boasted of them. To all work done by others, in his or their department, he gladly yielded recognition. Unhesitatingly he subordinated himself in every respect to De Sacy, and to Lane's knowledge of the Arabic, as (in his opinion) superior to his He was never ambitious of empty honors, he never sought to assert himself. own. What was called Fleischer's school, can scarcely be said any longer to exist as such. Arabic studies, the preponderance of which formed the most distinguishing mark of its unity, have been curtailed in Germany. A cruel fate has prematurely removed the very best philologists of Fleischer's school: Ralfs, Loth, Spitta, and, furthermore Kosut and Huber. Some of us have struck out on new paths; general interest has been diverted to Assyriological research and to comparative philology. The leadership in the Arabic domain is about to pass over to the Dutch school. But it matters not what we do, if only we emulate the example of "our sheikh," and do disinterested, honest, diligent, conscientious, and modest work, in whatever is within the reach of our limited ability. A MEMOIR OF GUSTAV ROBERT KIRCHHOFF.* BY ROBERT VON HELMHOLTZ. On the 20th day of Getober of the past year (1887) we bade our last farewells to Gustav R. Kirchhoff in St. Matthew's Cemetery at Berlin. Natural science has lost one of its mightiest promoters, Germany is bereft of one of her keenest thinkers, the youth lament their honored, brilliant master, and his friends mourn over a man who belonged to the best, in the true meaning of this word. While Kirchhoff's works made his name immortal, so that wherever physics is taught he will be mentioned, such were his modesty and simplicity that his own person was hidden behind the object to which he devoted his life, and if we except his colleagues and those who had the fortune to be near him, there were very few who knew more than that Kirchhoff was the illustrious discoverer of spectrum analysis. Let one of his students be permitted to attempt to do what he would never have undertaken himself and what even would have been painful to him while he lived,-to draw a picture of his work not in its pure, abstract form, destitute of all earthly vesture, as he produced it, but rather in connection with his personal life, and as a fruit of his personal genius. Gustav R. Kirchhoff was a professor of mathematical physics. I mention this first, not because it is the main fact which would stand first in a biographical dictionary, but because mathematical physics is a science of which only he who was born to it can become an adept. There are vocations in life, there are branches of science that do not allow us to infer what spirit animates their adepts. In certain regions of abstract science however, whoever wants to penetrate into them, must have faculties and dispositions of definite nature and bias, otherwise he will not even cross the threshold that leads to them. Pure mathematics is such a science. Every-day experience teaches us that only a small proportion of students are endowed with a genius for it. It is more difficult to say on what powers of the human mind such a genius rests. Mathematics is logic applied to numbers and extensive magnitudes. It requires accordingly a great power of abstraction and the faculty of intuitive perception of relations of magnitudes. At any *From the Deutsche Rundschau, February, 1888: vol. XIV, pp. 232–245. rate, just because the technics of pure logical thinking have to be developed to a great extent, the perceptive faculty of a mathematician, his judgment and his representation of things are of a peculiar kind. The natural philosopher requires however another faculty still, I mean the faculty of observation. Every one whose work rests on observation is a student of nature in the widest meaning of this word; the physician, the traveller, the collector. To observe is to notice, and to collect what you have noticed. In proportion however as the collecting of things is done according to higher and higher standards, observation comes nearer to thinking, collecting approaches interpretation, and natural history verges into exact study of nature. The adepts of natural science work not only through the senses by means of observation, but also by means of the logical faculty of drawing inference. They differ from mathematicians chiefly in the material for their thinking being given in the external world and that they must have the talent to find it there, while the foundations of mathematics seem to be given a priori. Mathematics is the most convenient instrument in the exact science of nature because it is the tongue in which the latter can express its conclusions in the quickest and most precise way. That is why the exact study of nature becomes more and more mathematical; physics, after astronomy, has made the most progress in this direction; chemistry is about to follow it. Speaking generally, the greatest physicist nowadays will be he who is endowed equally with the gifts of observation and with logical precision of thinking, and has mastered experiment as well as mathematics. According to the pre-eminence of the one or the other faculty the place of each investigator will be nearer to the observers of nature or to the thinkers about nature. Both kinds are necessary, the latter is more seldom met with, there are more good observers than good thinkers. Gustav R. Kirchhoff belongs rather, according to his nature, to the great thinkers, and still his greatest and most celebrated discovery is a discovery of observation. He was one of the greatest natural philosophers just because he was a mathematical physicist in the above-mentioned sense. The life of Kirchhoff was that of a thinker, too. He did not travel all over the world to see nature in the splendid attire of her multifarious productions, like Humboldt or Darwin; he did not work his way to theory through a school of purely practical life, like Faraday or Siemens. No more did he pass his life in the whirlpool of historical or social events. He accomplished his work quietly in the externally serene, but internally the more active, abodes of science,-in the lecture-rooms and laboratories of several German universities. Whoever wants to know him must follow him thither into spheres of thought that lie afar off from the interests of the day. Gustav R. Kirchhoff, son of the lawyer, was born (1824), brought up, and educated at Königsberg, the "City of Pure Reason." According to a certificate from the Kneiphof High-school, he wished to devote him |