PolyOz "the positive feelings one gets when a lover is enjoying another relationship. Sometimes called the opposite or flip side of jealousy." They comment that compersion can coexist with jealous feelings.
The Polyamory society "the feeling of taking joy in the joy that others you love share among themselves, especially taking joy in the knowledge that your beloveds are expressing their love for one another".
The InnKeeper "A feeling of joy when a loved one invests in and takes pleasure from another romantic or sexual relationship. ... Compersion does not specifically refer to joy regarding the sexual activity of one's partner, but refers instead to joy at the relationship with another romantic or sexual partner. It's analogous to the joy parents feel when their children get married, or to the happiness felt between best friends when they find a partner."
From Opening Up, Serena Anderlini-D'Onofrio writes that compersion is, in part, "the ability to turn jealousy's negative feelings into acceptance of, and vicarious enjoyment for, a lover's joy". (p. 175)
The railway first came to Berlin in 1838, with the opening of the Potsdamer Bahnhof, terminus of a 26 km line linking the city with Potsdam, opened throughout by 29 October (in 1848 the line would be extended to Magdeburg and beyond). Since the city authorities would not allow the new line to breach the customs wall, still standing at the time, it had to stop just short, at Potsdamer Platz, but it was this that kick-started the real transformation of the area, into the bustling focal point that Potsdamer Platz would eventually become.
Just three years later a second railway terminus opened in the vicinity. Located 600 metres to the southeast, with a front facade facing Askanischer Platz, the Anhalter Bahnhof was the Berlin terminus of a line opened on 1 July 1841, as far as Jterbog and later extended to Dessau, Kothen and beyond.
Both termini began life as fairly modest affairs, but in order to cope with increasing demands both went on to much bigger and better things in later years, a new Potsdamer Bahnhof, destined to be Berlin's busiest station, opening on 30 August 1872 and a new Anhalter Bahnhof, destined to be the city's biggest and finest, following on 15 June 1880. This latter station benefitted greatly from the closure of a short-lived third terminus in the area the Dresdner Bahnhof, located south of the Landwehrkanal, which lasted from 17 June 1875 until 15 October 1882.
In addition, a railway line once ran through Potsdamer Platz itself. This was a connecting line opened in October 1851 and running around the city just inside the customs wall, crossing numerous streets and squares at street level, and whose purpose was to allow goods to be transported between the various Berlin stations, thus creating a hated traffic obstruction that lasted for twenty years. Half a dozen or more times a day, Potsdamer Platz ground to a halt while a train of 60 to 100 wagons trundled through at walking pace preceded by a railway official ringing a bell. The construction of the Ringbahn around the city's perimeter, linked to all the major stations, allowed the connecting line to be scrapped in 1871, although the Ringbahn itself was not complete and open for all traffic until 15 November 1877.
In later years Potsdamer Platz was served by both of Berlin's two local rail systems. The U-Bahn arrived first, from the south; begun on 10 September 1896, it opened on 18 February 1902, with a new and better sited station being provided on 29 September 1907, and the line itself being extended north and east on 1 October 1908. In 1939 the S-Bahn followed, its North-South Link between Unter den Linden and Yorckstrae opening in stages during the year, the Potsdamer Platz S-Bahn station itself opening on 15 April.
By the second half of the 19th century, Berlin had been growing at a tremendous rate for some time, but its growth accelerated even faster after the city became the capital of the new German Empire on 18 January 1871. Potsdamer Platz and neighbouring Leipziger Platz really started coming into their own from this time on. Now firmly in the centre of a metropolis whose population eventually reached 4.4 million, making it the third largest city in the world after London and New York, the area was ready to take on its most celebrated role. Vast hotels and department stores, hundreds of smaller shops, theatres, dance-halls, cafs, restaurants, bars, beer palaces, wine-houses and clubs, all started to appear. Some of these places became internationally known.
Also, a very large government presence, with many German imperial departments, Prussian state authorities and their various sub-departments, came into the area, taking over 26 former palaces and aristocratic mansions in Leipziger Platz, Leipziger Strae and Wilhelmstrae. Even the Reichstag itself, the German Parliament, occupied the former home of the family of composer Felix Mendelssohn (180947) in Leipziger Strae before moving in 1894 to the vast new edifice near the Brandenburg Gate, erected by Paul Wallot (18411912). Next door, the Herrenhaus, or Prussian House of Lords (the Upper House of the Prussian State Parliament), occupied a former porcelain factory for a while, before moving to an impressive new building erected on the site of the former Mendelssohn family home in 18991904 by Friedrich Schulze Colditz (18431912). This building backed on to an equally grand edifice in the next street (Prinz-Albrecht-Strae), also by Colditz, that had been built for the Preuischer Landtag (the Prussian Lower House), in 1892-9.
Potsdamer Platz was also the location of Germany's first electric street lights, installed in 1882 by the electrical giant Siemens, founded and based in the city.