In September 1828 Chopin, while still a student, visited Berlin with a family friend, zoologist Feliks Jarocki, enjoying operas directed by Gaspare Spontini and attending concerts by Carl Friedrich Zelter, Felix Mendelssohn and other celebrities. On an 1829 return trip to Berlin, he was a guest of Prince Antoni Radziwi, governor of the Grand Duchy of Posenhimself an accomplished composer and aspiring cellist. For the prince and his pianist daughter Wanda, he composed his Introduction and Polonaise brillante in C major for cello and piano, Op. 3.
In 1829 on a trip back to Berlin Chopin was a guest of who?
Prince Antoni Radziwi

Historically, AC motors were used for single or double speed elevator machines on the grounds of cost and lower usage applications where car speed and passenger comfort were less of an issue, but for higher speed, larger capacity elevators, the need for infinitely variable speed control over the traction machine becomes an issue. Therefore, DC machines powered by an AC/DC motor generator were the preferred solution. The MG set also typically powered the relay controller of the elevator, which has the added advantage of electrically isolating the elevators from the rest of a building's electrical system, thus eliminating the transient power spikes in the building's electrical supply caused by the motors starting and stopping (causing lighting to dim every time the elevators are used for example), as well as interference to other electrical equipment caused by the arcing of the relay contactors in the control system.
What is a known advantage of the MG set?
electrically isolating the elevators from the rest of a building's electrical system

Combined with this influx of classical ideas was the invention of printing which facilitated dissemination of the printed word and democratized learning. These two things would later lead to the Protestant Reformation. Toward the end of the period, an era of discovery began (Age of Discovery). The rise of the Ottoman Empire, culminating in the Fall of Constantinople in 1453, eroded the last remnants of the Byzantine Empire and cut off trading possibilities with the east. Europeans were forced to seek new trading routes, leading to the expedition of Columbus to the Americas in 1492, and Vasco da Gama's circumnavigation of India and Africa in 1498. Their discoveries strengthened the economy and power of European nations.
In what year did Vasco da Gama sail around India and Africa?
1498