Henry Green applies for a patent -- from Unionville

1. Green would apply for another patent for a level on August 4, 1890.
2. Green would receive his patent, No. 438,541, on October 14, 1890.

A spirit level in 1889 is exactly what it is today:  a tool for checking whether a surface is level or plumb.

United States Patent Office, "Spirit Level," Patent No. 438,541, October 14, 1890.