Anders Celsius magnitude (a measure of brightness) of certain stars. This was the first attempt to measure the intensity of starlight with a tool other than the human eye. He made observations of eclipses and various astronomical objects and published catalogues of carefully determined magnitudes for some 300 stars using his own photometric system (mean error=0.4 mag). Celsius was the first to perform and publish careful experiments aiming at the definition of an international temperature scale on scientific grounds. In his Swedish paper "Observations of two persistent degrees on a thermometer" he reports on experiments to check that the freezing point is
Stephen Alexander (astronomer) Stephen Alexander (astronomer) Stephen Alexander (September 1, 1806 – June 25, 1883) was a noted astronomer and educator. He was born in Schenectady, New York. He was the brother-in-law of Joseph Henry, the first secretary of the Smithsonian, and worked closely with him. He graduated from Union College in 1824. He became a tutor in mathematics at Princeton University in 1832; he would later become professor of astronomy and mathematics and advocate for the construction of Princeton's first observatory. Alexander relied on the assistance of a free African American man named Alfred Scudder, who worked for him at Princeton during