You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Nikola_Tesla

Context:
Tesla also explained the principles of the rotating magnetic field in an induction motor by demonstrating how to make a copper egg stand on end using a device he constructed known as the Egg of Columbus.

Question:
What was Tesla's device called?

Egg of Columbus