A correlation is a single numerical value that is used to describe the relationship between two variables. All correlations have strength and direction. When two variables have a positive correlation, that means the two variables move in the same direction. The closer a positive correlation is to 1, the stronger it is.
William Gilbert discovered electricity, not Nikola Tesla. Nikola Tesla invented things. not discovered electricity. Again, William Gilbert discovered it and named it. He did this in the 1600s. It wasn't Nikola Tesla.
It was during the 19th century that pioneers such as Alessandro Volta, Michael Faraday, Joseph Henry, and Thomas Edison figured out the secrets of electricity, how to produce it, and how to make it do useful things.