Windmuller's connections with these men were consistent. He joined with them to agitate for political reform, promote social welfare, and seek cultural advancement. Some he named in his published writings as the best of the city's German immigrants. The names of others show up in news accounts of public meetings, lists of leaders of charitable causes, and accounts of banquets in honor of one of their number.
In later years he would discover that he shared with four of these exceptional men the experience of participating in the German Revolutions of 1848. The spontaneous mass demonstrations in Germany's cities which occurred that year aimed to oust the autocratic governments of the German states and achieve basic liberal freedoms such as those enjoyed by British subjects and American citizens (freedom of assembly, freedom of the press, democratic elections of leaders). Despite the success of popular uprisings, the task of establishing a democratic constitution for a unified Germany proved to be too difficult for the Frankfort Assembly, which had emerged from the mass movement, but the turmoil did allow Prussia to become the dominant state and, under Bismarck's leadership, unification (though without a popularly-mandated constitution) did eventually come about.
Windmuller himself was only 13 at the time the mass uprisings began. He later said, "In 1848 the Parliament at Frankfort on the Main proposed Johann of Austria for Emperor of Germany and the Republicans in Munster had a jubilee in honor of the event. All but the conservatives decorated their houses. The Republican boys -- I was one of them --broke the windows in all the undecorated houses of the conservatives. My father was a conservative and I broke all his windows. Some of the boys were arrested but I escaped."
In 1848 Carl Schurz, six years older than Windmuller, was a 19-year-old university student. Influenced by a radical professor, he began writing passionate articles for a small daily newspaper in Bonn and in time became a leader within the student groups that participated in the revolt. After months of agitation, after Prussian troops had dispersed the Frankfort Assembly, Schurz took up arms against government forces. When the uprising proved to be a dismal failure, Schurz was forced to leave Germany. This is how he saw his situation: I was a fugitive, running away from the authorities... This was a singularly uncomfortable feeling; but a much more hideous thought followed -- that I could not be proud of the act to which I owed my outlawry, although its purpose had been patriotic. The outcome had been miserable enough to make impossible my return to my friends, until the shame of it had been wiped out. But my profoundest grief was not with regard to myself. It was the knowledge that all the insurrectionary attempts in Prussia had failed." After spending most of a year in exile Schurz was able to replace his grief over this farcically romantic episode with an authentically romantic rescue of his imprisoned friend and former teacher. Although Schurz, in his flight, had been able to evade arrest, this man, Gottfried Kinkel, had been captured and put in the impregnable Spandau Prison in Berlin. Schurz returned to Germany incognito to organize and personally direct a dramatic escape. Schurz's account of the daring escape is fascinating (you can read it here).
A bit older than Schurz, Oswald Ottendorfer was 22 and a university student in Vienna when the Revolutions of 1848 began. He and Schurz came from opposite ends of German-speaking Europe but their upbringings and experiences in the revolutions were similar. Both received excellent educations which they interrupted in 1848 to join the fight in their part of the world, both here highly articulate in speech and writing, both exiled themselves to avoid arrest and probable execution, and both returned from exile to rescue imprisoned comrades.
In March 1848 Ottendorfer joined the Viennese students' legion to fight for the newly-installed liberal regime. Later that year, having served briefly in a war against Denmark and then in Hungary, he returned to Vienna became attached to a mobile guard composed largely of newspapermen. The battalion was at first able to resist attacks from an invading contingent of the Austrian army but was later completely crushed. Of this period a contemporary biographer says "All through the stirring scenes in Central Europe at that period young Ottendorfer bore an active and conspicuous part. The record of his hair-breadth escapes from death or imprisonment appears like a chapter of a wild romance. He finally assisted in the rescue of one of the leaders from a life imprisonment, escaped with him into Switzerland, and after encountering many difficulties came to the city of New York in 1849, and sought literary employment."
Henry Villard was born the same year as Windmuller. Like Windmuller his family suffered privation when his father lost his job when a revolutionary government took power during the upheavals that began in 1848. Like Windmuller, he sided with the rebels against his conservative father and repeatedly disobeyed his father's wishes. At age 14, he actually served in the local militia when the Prussian army attacked to regain control of his home state of Rhenish Bavaria. Unlike Windmuller, however, he was able to graduate from secondary school and attain a couple of years of university education. Then in 1853, like Windmuller, he decided to emigrate and set sail for New York. Unlike Schurz and Ottendorfer, he was not forced into exile by direct threat of imprisonment but, like Windmuller, was determined to escape what he considered to be an intolerably oppressive atmosphere at home and to make his own way in the new world.
Villard's first days as an immigrant were very much like Windmuller's. This is from Villard's memoirs (1904): "MY landing upon American soil took place under anything but auspicious circumstances. I was utterly destitute of money, had but a limited supply of wearing apparel, and that not suited to the approaching cold season, and I literally did not know a single person in New York or elsewhere in the Eastern States to whom I could apply for help and counsel. To crown all, I could not speak a word of English... [I] began my search for something to do by which I could earn my daily bread. In the pursuit of my object I saw much of New York. The city had then only about three hundred thousand inhabitants, but, unless my memory deceives me, its leading business streets presented as striking and stunning a picture of intense commercial activity as to-day. The sidewalks on Broadway were certainly very crowded with people, and the street proper jammed full of vehicles of every description. But, of course, the city had comparatively small dimensions. Fourteenth Street was the limit of animated street-life. Beyond it the rows of buildings began to thin out, and above Twenty-third Street things still had an open-country appearance." 
Compare this memory of Villard's with Windmuller's letter home, written in 1855 about his experiences of 1853: "The unfriendly weather and the cold reception from our relatives ... brought forth feelings of abandonment. I received from my cousin a few purses [and other merchandise] with which I eagerly went to business. I went to the houses of the wealthy (on Fifth Avenue, a row of palaces) and asked for the 'lady of the house.' I was usually turned away but sometimes invited in and very seldom I sold something. Nevertheless for a time I did well and earned a few dollars a day but after a while my luck ran out and also my money. I then tried [to sell] other things, liquor, wine, and tea; but I had no luck or patience with these... Sad, but not giving up my courage, I wandered through the streets of the metropolis where you see the greatest poverty and the greatest luxury. New York is a great city and not without justification is called the Empire City. The best products and the most beautiful works of art created by the civilized world find a market here. The flags of every nation are represented in the harbor and I believe that every nation or people on this beautiful earth is found on the streets of New York. The Spanish with their grandezza, the French with their inexhaustible politeness, the reserved Dutch, the attentive Chinese, the British with their decisiveness, all these nationalities are represented here. How amazed you would be if from your quiet Muenster you would find yourself transported to Broadway, the premier street of New York. Your ears would become deaf from the noise of wagons which are all bunched up but still move in an orderly fashion; your eyes would become blind from the wealth and luxury of the Italian marble. You would be astonished to see the busy populace which runs as if it needed to reach the end of the world. I had enough time to observe this; for days I looked at this spectacle, however my thoughts were elsewhere. I began to think how I could make a living."
Born a few years before and dying a few years after Louis Windmuller, Abraham Jacobi was the only one of these five Forty-Eighters who was imprisoned for what he said and did. His family was less well off than Windmuller's but they succeeded nonetheless in supporting him through a extensive education which culminated, at age 21, in a degree as doctor of medicine. As a university student he joined the Communist League, in which Marx and Engels were also involved and for which they wrote the Communist Manifesto. Arrested for plotting to overthrow the Prussian king, he spent eighteen months in prison awaiting trial, but was finally acquitted. Jacobi's association with Germany's nascent communism as well as his service in a revolutionary militia again earned him imprisonment as an accused and, in the end, a term in prison as convicted revolutionary. In 1852 he served six months for seditious speech and, with the help of a sympathetic jailer, managed to exile himself before another charge could be leveled against him. A modern biographer says that when Jacobi decided to emigrate to the United States in 1853 (the same year as Windmuller), he told Marx "I'll try it over there" and on arriving in New York immediately joined the socialist German trades union movement.
In 1900, at a banquet at Delmonico's in New York City which was given to honor Jacobi, Schurz spoke of this period in their lives:
I have been asked to speak of Dr. Jacobi as a citizen, and I may say that the manner in which he got into jail in the old country — for I have to admit the fact that he did serve two years in state prisons, whatever you may at the first blush think of it — indicated at that early day very clearly what kind of a citizen he would make in this Republic. He was one of the young men of that period who had conceived certain ideals of right, justice, honor, liberty, popular government — but which they cherished and believed in with the fullest sincerity, and for which they were ready to work and to suffer, and, if necessary, to die. Theirs was a devotion, too, wholly free from self-seeking ambition — a devotion which found all its aims and aspirations and rewards within itself.The five friends I've briefly profiled here were all German idealists who while young, some still only boys, learned to question, then resist, then attack the repressive regimes under which they lived. Failing to defeat a system based on what Windmuller called "tyrannical laws and feudal prejudices," they came to New York where all of them did well, though no two in the same way. As Schurz said of Jacobi, they all had to face the fact that their revolutionary acts in Germany might prevent them from achieving success in America. Despite this, they all did succeed and in doing so none renounced his youthful radicalism.
Of that class of young men he was one, struggling with poverty and no end of other discouragements in his laborious effort to become a good physician. He knew well that political activity could not possibly help him in reaching that end, but might rather become a serious obstacle in his path. Neither had he any craving to see his name in the newspapers, or to strike an attitude before the public. But moved by a simple sense of duty to his fellow-men, he associated himself, and unostentatiously cooperated with others in advocating and propagating the principles which formed his political creed. His convictions might have been honestly modified or changed by super-study, or larger experience, but they would not yield an inch to the reductions of fortunes, or to the frowns or favors of power. And as nothing could prevail upon him to renounce or even equivocate about the faith he honestly held, he went to jail for it, suffering his martyrdom with that inflexible and, at the same time, modest fortitude which is the touchstone of true manhood. Thus to have served a term in prison was with him a mark of fidelity to his conception of his duty as a citizen.
-- Carl Schurz, Response to the toast, "The Citizen," at a complimentary dinner at Delmonico's, New York City, May 5, 1900, tendered to Dr. Jacobi on the occasion of the seventieth anniversary of his birth, in Speeches, correspondence and political papers of Carl Schurz (G.P. Putnam's Sons, 1913)
Here are portraits of the five men.
I put Abraham Jacobi first because his face was the most interesting.
The following all come from Geschichte des deutschthums von New York von 1848 bis auf die gegenwart By Theodor Lemke (T. Lemke, 1891).
This is the title page of the source of these photos.
Geschichte des deutschthums von New York von 1848 bis auf die gegenwart By Theodor Lemke (T. Lemke, 1891)
The German element in the United States by Albert Bernhardt Faust, Volume 2 (Houghton Mifflin company, 1909)
CARL SCHURZ, Balch Institute for Ethnic Studies
WHY IMMIGRATION OUGHT NOT TO BE RESTRICTED, a letter to the editor, New York Times, December 30, 1892, by Louis Windmuller
Carl Schurz, a biography by Hans Louis Trefousse (Fordham Univ Press, 1998)
Modern History Sourcebook: Documents of German Unification, 1848-1871
The Reminiscences of Carl Schurz, Volume One (1829-1852)
OTTENDORFER, Oswald 1826 - 1900
VILLARD, Henry (1835-1900)
Ferdinand Hilgard on spartacus
Memoirs of Henry Villard, journalist and financier, 1835-1900 edited by Fanny Garrison Villard (Houghton, Mifflin and Company, 1904)
Abraham Jacobi in wikipedia
Abraham Jacobi Biography (1830-1919) in faqs.org
Abraham Jacobi on famousamericans.net
"Abraham Jacobi — A Sketch" by Algernon Thomas Bristow in New York State journal of medicine, Vol. 10, No. 5, May 1910 (Medical Society of the State of New York, 1910)
Formative years: children's health in the United States, 1880-2000 by Howard Markel (University of Michigan Press, 2002)
Rhineland Radicals: The Democratic Movement and the Revolution of 1848-1849 by Jonathan Sperber (Princeton University Press, 1992)
"The Grandson of the Liberator" by R.L. Duffus, American Mercury Magazine edited by H. L. Mencken, September to December 1927 (Kessinger Publishing, 2003)
"DR. ABRAM JACOBI," Response to the toast, "The Citizen," at a complimentary dinner at Delmonico's, New York City, May 5, 1900, tendered to Dr. Jacobi on the occasion of the seventieth anniversary of his birth, in Speeches, correspondence and political papers of Carl Schurz Volume 6 (G.P. Putnam's Sons, 1913)
"ABRAHAM JACOBI — A SKETCH," by Algernon Thomas Bristow in (New York State journal of medicine, Vol 10, No. 5, May, 1910 (Medical Society of the State of New York, 1910)
 The quote comes from Leslie's history of the greater New York by Daniel Van Pelt (New York, Arkell Pub. Co., 1898). It is echoed in most of the other biographic dictionaries.
 I'll let one example stand for all: Charles Hauselt was well known in his day and not since. Two-thousand souls showed up for his funeral including many political dignitaries and heads of local civic organizations. The New York Times reported that "several aged Germans were so much overcome by the close atmosphere that they had to be assisted to the open air." (FUNERAL OF MR. HAUSELT.; TWO THOUSAND PERSONS ATTEND THE SERVICES AT ST. MATTHEW'S, New York Times, February 12, 1890.) A few days after the funeral, Hauselt's memory was honored at a large gathering at Steinway Hall. The Times reported said, "The great esteem in which Charles Hauselt was held, not only by his fellow-countrymen in this city but by all who had ever had relations with him, was still further testified to yesterday by the memorial services which where held in the afternoon at Steinway Hall." (HONORING CHARLES HAUSELT.; STEINWAY HALL CROWDED AT HIS MEMORIAL SERVICES., New York Times, February 17, 1890.) The Times index lists 55 instances in which it appeared in articles, and all but one in papers published prior to 1908. This Google Ngram for Charles Hauselt shows that his surname appeared in many books during his life and very few times in recent decades (the uptick in the last 20 years is for other people named Hauselt).
 See this previous post on prominent German-Americans.
Windmuller said this in a proposal for the city to erect a monument to the poet Goethe. Brooklyn Daily Eagle, November 24, 1909.
 "Between 1845 and 1854 over one million German citizens left their homes and emigrated, many of them as a result of the failed revolution of 1848 and its aftermath. The 'Forty-Eighters' who came to the United States both for political and economic reasons went through different stages of adaptation to the new country. The immigrants contributed to the political, social and cultural life of their new homeland by transforming staid communities on the East coast, by founding new settlements in the Midwest and West, and by swelling the number of politically conscious artisans and workers in the big cities. Their voting power and personal sacrifices were of great importance in the abolition of slavery in the U.S. They participated in the debate about the women's vote and in stressing the concepts of free and general education."
-- Carl Schurz and the Forty-Eighters in America.
 Carl Schurz wrote that the Frankfort Parliament suffered from "an overabundance of learning and virtue and a want of that political experience and sagacity." -- Reminiscences of Carl Schurz, Volume One (1829-1852), CHAPTER VI. Germany (1848-1871) on the Open Door web site gives a succinct summary. See also Modern History Sourcebook: Documents of German Unification, 1848-1871
 The quote comes from: Herr Windmuller Confesses, Distinguished New Yorker Breaks Down Under Cross Examination, The Sun, Saturday, June 30, 1906.
 Carl Schurz's parents supported his determination to take up arms in this last-ditch action. Of his mother's response, he later wrote, "Like the Spartan woman or the Roman matron of whom we read, my mother went to the room where my sword hung and gave it to me with the one admonition that I should use it with honor. And nothing could have been further from her mind than the thought that in this act there was something heroic." (Reminiscences of Carl Schurz, Volume One (1829-1852), CHAPTER VI.)
 Same source.
 To his credit, Schurz was deeply embarrassed by the effusive outpourings that followed from his rescue of Kinkel.
Although I had received in Rostock, in Edinburgh, and in London, in small circles of friends, praise of the warmest kind, I was not a little astonished and embarrassed when I learned in Paris of the sensation created by the liberation of Kinkel... It had become generally known that I, a student of the university of Bonn, had taken a somewhat important part in that affair... The Liberal newspapers in Germany had vied with one another in romantic stories about the adventure... Several newspapers put before their readers my biography, which consisted in great part of fantastic inventions, inasmuch as there was but little to say of my young life. I even became the subject of poetic effusions, which celebrated me in all sorts of sentimental exaggeration. My parents, as they afterwards wrote me, were fairly flooded with congratulations, which in great part came from persons entirely unknown to them... In every company in which I showed myself I was asked time and again: "How did you succeed in carrying out this bold stroke? Tell us." Inasmuch as I could not tell the whole truth, I preferred to tell nothing. New legends were invented which if possible were still more fantastic than the old ones. This was so oppressive to me that I became very much averse to going into society, and I fear that I sometimes repelled those who came to me and pressed me with questions in an almost unfriendly manner. The quote comes from History of New York City, embracing an outline sketch of events from 1609 to 1830, and a full account of its development from 1830 to 1884, by Benson John Lossing, Volume 2, (Perine Engraving and Pub. Co., 1884). Another biographer gives some further detail:
-- same source.
Of the few students who escaped in safety from the Austrian capital, Mr. Ottendorfer was one. After three days and nights of hiding in the chimney of an old book store, the young man made his way to Saxony, only to return, under an assumed name, with others, to the capital of Bohemia to concert another uprising. The movement was discovered, however, and the students fled to Dresden, where, in May 1849, they took part in another revolution and held possession of the city for nearly a week. This was a serious affair and ended in the recapture of the city by Prussian troops, hastily summoned by the King of Saxony. The students sought to escape to Thuringia, but those who left the city were all taken. Like their compatriots in Vienna, many were put to death an others sentenced to long imprisonment. Mr. Ottendorfer escaped by an accident. He had spent several days and nights without rest and, owing to physical exhaustion, did not awaken until noon, when he found Dresden full of Prussian soldiers. After a few days of concealment, he managed to reach Frankfort unobserved. But agitation continued and Mr. Ottendorfer would have taken part in the battle of Waghaeusel had he not been stricken down with typhoid fever in Heidelberg. His last exploit, undertaken after three months of hiding, was the rescue of Steck, who had been sentenced for life and incarcerated in the castle of Bruchsal. With his comrades and Steck, he escaped safely to Switzerland. At twenty-four, Mr. Ottendorfer had passed trough scenes of tragic adventure, such as fall to the lot of few men of his age. His hopes had been frustrated and he then resolved to begin life anew in Vienna. From this he was dissuaded by friends, who predicted certain death should he return to the scene of his revolutionary labours. In this emergency, he finally decided to emigrate to the United States. With the aid of friends, he passed through Poland and in 1850, landed in New York City. His means were small but he found a large, liberty-loving, German element in the city, who welcomed the young agitator with great cordiality. Memoirs of Henry Villard, journalist and financier, 1835-1900 edited by Fanny Garrison Villard (Houghton, Mifflin and Company, 1904)
-- OTTENDORFER, Oswald 1826 - 1900 from the Seilern Family genealogy.
 You can read the whole letter in English here and in German in this blog post.
 See On The History of the Communist League by Frederick Engels, in Sozialdemokrat November 1885.
 From a biographic sketch that appeared late in Jacobi's life: "The Revolution had broken out meanwhile, in 1848. There were plenty of revolutionary and socialistic teachers in the Gymnasium with whom he was brought in contact, and consequently he soon became a member of one or more of the students' societies whose object was to revolutionize the world and incidentally Prussia. Like the traditional German student of the middle ages, he packed his knapsack after he had learned what he wanted at Griefswald, and went to Goettingen to learn pathological anatomy. There he worked with Virchow, and Woehler. He remained in Goettingen a year, and finding the clinics poor, again shouldered his knapsack, and staff in hand went to Bonn, where he stayed a year and a half, from which University he finally received his diploma. Then he went to Berlin to pass his State examination, but meantime, the police had heard of his dealings with the revolutionary party, and gobbled him up... In Cologne, he met ... Karl Marx, and his bosom friend, Frederick Engels... Some of the students of other universities died on the battle field and some were shot by the Prussians. Dr. Jacobi's name was found in the correspondence, so he was jailed with others to be tried for high treason and was sent to Cologne, where he cooled his heels and his temper for a year and a half behind the thick walls of a German fortress. From one quarter of a year to another his trial was postponed, but some less fortunate were imprisoned for five years, six years, seven years. Finally Jacobi was acquitted of high treason. He had spoken disrespectfully of the King and the government of Germany, however, and the Prussians couldn't stand that, so they convicted him of "lese majestat," and off he went to Minden to be imprisoned for six months... The jailer was his friend, and when the time for his release came, as he had heard that there was something still against Jacobi, he let him out early in the morning instead of in the evening, so he could escape. Jacobi was then twenty-three years old. He went over the mountains to see his mother, then escaped to Hamburg, from whence in ten or twelve days he took ship for England." -- "ABRAHAM JACOBI — A SKETCH," by Algernon Thomas Bristow in (New York State journal of medicine, Vol 10, No. 5, May, 1910 (Medical Society of the State of New York, 1910)
 In this speech Schurz also described his first meeting with Jacobi: "Of Dr. Jacobi's friends assembled here, I am, no doubt, the oldest, probably the oldest in years, and certainly the oldest in friendship — for that friendship can look back upon just a half century of uninterrupted, and, I may add, unclouded duration. It was in the year 1850, in the German University town of Bonn-on-the-Rhine, that we first met. He was then still a student of medicine in regular standing. I was already an exile, but had secretly come back to Germany, engaged in a somewhat adventurous enterprise connected with the revolutionary movements of that period — an enterprise which made it necessary to conceal my whereabouts from those in power, with whom my relations were at the time, to speak within bounds, somewhat strained. I had the best reasons for desiring to avoid persons whose ill-will or indiscretion might have brought me into touch with the constituted authorities. It was then that a 'mutual friend' introduced Jacobi and me to each other during a dark night in an out-of-the-way little garden house, having described him to me as a young man who could be absolutely depended upon in every respect and under all circumstances. And as the man who can be depended upon in every respect and under all circumstances, I have known and loved him ever since; and if we could live together another half century, I should be ready to vouch for him in that sense every day of the year and every hour of the day. At the period of which I have been speaking our intercourse was very short. We travelled together a day or so — he going to Schleswig-Holstein where, as a budding physician, he expected to do service in the capacity of a volunteer surgeon in the war then going on, and I to the field of my operations." -- "DR. ABRAM JACOBI," Response to the toast, "The Citizen," at a complimentary dinner at Delmonico's, New York City, May 5, 1900, tendered to Dr. Jacobi on the occasion of the seventieth anniversary of his birth, in Speeches, correspondence and political papers of Carl Schurz Volume 6 (G.P. Putnam's Sons, 1913)
 Windmuller wrote this phrase in: WHY IMMIGRATION OUGHT NOT TO BE RESTRICTED, a letter to the editor, New York Times, December 30, 1892.