John Louis Emil Dreyer (13 February 1852 – 14 September 1926), also Johan Ludvig Emil Dreyer, was a Danish astronomer who spent most of his career working in Ireland. He spent the last decade of his life in Oxford, England.
There are several distinct phenomena that can be used to measure mass. Although some theorists have speculated that some of these phenomena could be independent of each other, current experiments have found no difference in results regardless of how it is measured